Friday
February 24, 2017

Homework Help: Science: Chemistry

Recent Homework Questions About Chemistry

chemistry
how many unpeeled electrons are in this configuration 1s2 2s2 2p6 3s2 3p3
Wednesday, January 18, 2017 by Emmanuel

Chemistry help??!
A student reduces the temperature from a 300 cm3 balloon from 60°C to 20°C. What will the new volume of the balloon be? 264 cm3 <my answer choice 100 cm3 300 cm3 341 cm3
Wednesday, January 18, 2017 by Vee

chemistry
which characteristics of solid, a liquid, and a gas are exhibited by each of the following substances? how would you classify each substance? A. a bowl of pudding will be solid and B. a bucketful of sand wiil be solid
Wednesday, January 18, 2017 by eunice

chemistry
when water boils, there is bubbles that rise to the surface of the water. What is inside these bubbles? air
Wednesday, January 18, 2017 by eunice

Chemistry
What is the oxidation state of Fe in Fe(CO)5
Wednesday, January 18, 2017 by Anonymous

chemistry
The molecular formula of 2.68g hydrated sodium sulphate is Na2SO4.nH2O.If the mass loss on heating is 1.26g then calculate the value of n.
Wednesday, January 18, 2017 by Farha

Chemistry
why homemade ice cream normally weighs twice the amount of commercially made ice cream
Tuesday, January 17, 2017 by Denya

chemistry
The following unbalanced equation describes the reaction that can occur when lead (II) sulfide reacts with oxygen gas to produce lead (II) oxide and sulfur dioxide gas: PbS + O2  PbO + SO2. all i need help on is explaination of the electron transfers that would happen in ...
Tuesday, January 17, 2017 by amtonio

Chemistry
Assume that 5.00 grams of zinc react with excess HCl according to the following equation: Zn + 2HCl = ZnCl2 + H2 The hydrogen was collected over water at 20.0C and the prssure of the atmosphere is 751 mmHg. The pressure of the water vapor at 20C is 17.5 mmHg. How many moles of...
Monday, January 16, 2017 by Michael

math sets
out of 320 students at a university,190 taking math,235 taking chemistry and 120 taking physics.125 are taking both chemistry and math,95 taking both chemistry AND PHYSIC,55 TAKING BOTH MATH AND PHYSICS.HOW MANY ARE TAKING ALL THE THREE SUBJECTS
Monday, January 16, 2017 by kelvin

Chemistry
How many moles of H are there in 8.9 moles of C4H8O2?
Monday, January 16, 2017 by Ricardo

Chemistry
How many moles of Cl ions are there in 8.5 moles of CaCl2 ?
Monday, January 16, 2017 by Ricardo

Chemistry
How to make 100 mL of 100mM of Tris HCl and 100 mL of 100mM of Tris Base. Follow the pH of the resulting combined solution as it is heated from 4 to 50 degrees Celsius. I did not use the HH equation in this problem. I started with just converting to moles needed and then to ...
Sunday, January 15, 2017 by Aarya Singh

Chemistry
How to Prepare 500mL a 50 mM pH 6 Citrate buffer starting from citric acid as the sole source of conjugate base I used the HH equation and got that citric acid concentration would be 0.035M, when converted to moles would be 3.362g. Then I was planning to add that amount to a ...
Sunday, January 15, 2017 by Aarya Singh

Chemistry
How is it possible that the atomic number increases in order, yet the atomic masses do not? A. There is no relationship between the atomic number and mass of the atom. B. The masses of the protons for Te, I, and Xe have slightly different masses. C. Since the numbers of ...
Sunday, January 15, 2017 by cool

Chemistry
Which of the following best explains how relative atomic mass could be determined from the type of data available to Dalton? A. By determining the mass of oxygen contained in a sample of water, its exact atomic mass could be determined. B. By comparing the masses of hydrogen ...
Sunday, January 15, 2017 by cool

Chemistry
2.40 L of N2, at 25 ∘C and 1.89 atm , is mixed with 2.60 L of O2, at 25 ∘C and 0.245 atm , and the mixture allowed to react. N2(g)+O2(g)→2NO(g) How much NO, in grams, is produced?
Sunday, January 15, 2017 by Julio

Chemistry
If we were to fill a bottle with boiling hot water than place it in a bucket filled with cold water what would happen to the bottle and why? i know the bottle would get crushed inwards but whats the science behind this can someone explain?
Sunday, January 15, 2017 by Chem

Chemistry
I'm doing a lab where I have to identify the oxidization state of Iron. Here's the procedure I had to go through: Use 0.5 molar concentration of CuSO4, get another beaker and add 0.1 grams of Iron to it. Add the CuSO4 to the beaker with the Iron fillings. Wait for the reaction...
Sunday, January 15, 2017 by Alex Li

chemistry
Your living room measures 45 ft by 62 ft. The cost of the carpet is $21/square yard. How much will you spend on carpet
Sunday, January 15, 2017 by sharicka

chemistry
We have 1L of 0.1mol/l solution of ammonium chloride, with pKa 9.2 for NH4+/NH3 Place in an increasing order on a pKa axis the different conjugate acid /base pairs present in the solution. Write the equation of the different reactions that may take place
Sunday, January 15, 2017 by angy

Chemistry
Calculate enthalpy of the reaction ethene+hydrogen gives ethane are -1410KJ,-286kJ and -1560KJ respectively at 25°c
Sunday, January 15, 2017 by Anonymous

Chemistry
In a certain reaction 0.20g of hydrogen gas combines with 3.20g of oxygen gas.if the relative molecular mass of the compound is 34.0 find its molecular formula (H=1,O=16).
Sunday, January 15, 2017 by feyonce

Chemistry - Enthalpy
When a 37.00 g silver spoon, initially at room temperature, is placed into 250.0mL of 90.00oC tea, it reaches a temperature of 85.00°C. The spoon will have gained ? J of thermal energy. I got 5237.5 Joules as (mass)x(specific heat capacity)x(Temperature change)=Heat, which ...
Saturday, January 14, 2017 by PleaseHelp

Chemistry
What will burning of .3 liters of C2H2 produce?
Saturday, January 14, 2017 by Ron

chemistry
Calculate pH of 6ml of 3M HNO3 diluted to 18 litres of water
Saturday, January 14, 2017 by Frederick

chemistry
1) Copy and complete: Two particles can react together only if they …… and the …… has enough …… to be ……. 2) What is meant by: a a successful collision? b an unsuccessful collision? 3) Reaction between magnesium and acid speeds up when: a)the concentration of ...
Saturday, January 14, 2017 by fiyin

Chemistry
If you had a basketball that was filled with mercury, about how much would it weigh? (The density of mercury is 13.6 grams per cubic centimeter.) First Hint: If you do not know the dimensions of a basketball, you should ESTIMATE them.
Saturday, January 14, 2017 by dsk

Chemistry
A large balloon contains 65.0 L of helium gas at 25 °C and a pressure of 745 mm Hg. The balloon ascends to 3000 m, at which the external pressure has decreased by 30.%. What would be the volume of the balloon, assuming it expands so that the internal and external pressures ...
Friday, January 13, 2017 by Sav

chemistry
Calculate the energies of the states of hydrogen atom with n=2 and n=3
Friday, January 13, 2017 by donald

Chemistry
Label the following changes as CHEMICAL or PHYSICAL change 1. Fat reacting with sodium hydroxide 2. Chemical A originally is buoyant in water; after it mixed with HCI, the new substance now sinks in water Label the following reactions as exothermic or endothermic 1. Ammonium ...
Friday, January 13, 2017 by Megan

Chemistry
I am having trouble on a chemistry question for my study guide I have researched it and can't get an answer I understand can someone please help me? Describe what happened when an Ag+ combined with Na2CO3. What does this indicate?
Thursday, January 12, 2017 by Sidney

Chemistry
What happens when equal volumes of 10^-5M of BaCl2 and 10^-5M of Na2SO4 are mixed at 25degree Celsius. Ksp of BaSO4=0.3×10^-10.
Thursday, January 12, 2017 by Barshali

Chemistry
0.001N NaoH calculate the ph
Thursday, January 12, 2017 by Rupesh

chemistry
25cm cubed of 0.250mol per litre of potasium carbonate was nuetralized 12.5cm cubed of ethanoic acid of unknown concentration.determine concentration of the acid
Wednesday, January 11, 2017 by jerry

chemistry
Calculate the energy required for ionization of electron from the ground state of hydrogen atom
Wednesday, January 11, 2017 by donald

chemistry
The reaction 2 NO(g) + O2(g) --> 2 NO2(g) is important in forming smog. Under certain conditions, the rate law for a the reaction is rate = 4.0 x 10-3 1/M2*s * [NO]2* [O2] What is the rate when [NO]=0.020 M and [O2]=0.035 M? a. 5.6 x 10-2 M/s b. 9.8 x 10-5 M/s c. 9.8 x 10-8...
Tuesday, January 10, 2017 by Jessie

chemistry
Calculate the concentration of KIO3(aq) present at the beginning of a reaction when 2.00 mL of 0.020 M KIO3(aq) is mixed with 8.00 mL of other solutions so the initial volume for the reacting mixture is 10.00 mL.
Tuesday, January 10, 2017 by Jessie

chemistry
Consider the reaction: N2(g) + 3 H2(g) --> 2 NH3(g). At a particular time, the nitrogen is being consumed at a rate of 0.60 moles/sec. At this same time, what is the rate at which ammonia is being formed? a. 3.0 mol/s b. 0.12 mol/s c. 0.30 mol/s d. 2.0 mol/s e. 1.2 mol/s
Tuesday, January 10, 2017 by Jessie

chemistry
The rate of a reaction A + 2B --> products is determined. When the concentration of A is 1.0 M, the rate of the reaction is 0.50 M/s. When the concentration of A is 0.50 M, the rate is 0.25 M/s. From this data, you can determine: a. that the reaction is second order in A. b...
Tuesday, January 10, 2017 by Jessie

chemistry
In a reaction, a chemist is observing the absorbance of CoCl2(aq) as a function of time to determine the rate at which it is being consumed in a reaction. At time t=10 s, the chemist determines that the concentration of CoCl2(aq) is 0.12 M. At time t=20 s, the chemist ...
Tuesday, January 10, 2017 by Jessie

Chemistry
why is a solution of copper sulfate and sulfuric acid required in corrosion testing? Won't the protons and the positive ions adhere to the metals surface and contaminant it?? Just a curious q. Thanks!
Tuesday, January 10, 2017 by Anonymous

Chemistry
Calculate the number of grams of the indicated element in the compound. a) lead in 63.8 g PbO2 b) carbon in 1.664 g (CH3)2CO
Tuesday, January 10, 2017 by Patricia

CHECK MY CHEMISTRY WORK PLEASE ASAP
1. You have been given a sample of unknown molarity. Calculate the molarity of a solution which has been prepared by dissolving 8.75 moles of sodium chloride in enough water to produce a solution of 6.22l. 2. You have a sample which consists of 428g sodium hydroxide (NaOH) ...
Tuesday, January 10, 2017 by David

Chemistry
What is an alcohol? Give a short definition. My answer: An organic compound in which one or more groups of hydroxyl is bonded to a chain of hydrocarbons. Do I need to change something of my answer to make it easier to understand? Thanks.
Tuesday, January 10, 2017 by Jenny

CHEMISTRY
You have been given a sample of unknown molarity. Calculate the molarity of a solution which has been prepared by dissolving 8.75 moles of sodium chloride in enough water to produce a solution of 6.22l. 2. You have a sample which consists of 428g sodium hydroxide (NaOH) ...
Tuesday, January 10, 2017 by David

Chemistry
For the following reactions, determine the equilibrium constant equation. 1) CO2(g) + H2(g) CO(g) + H2O(g) 2) 2NO(g) + 2H2(g) N2(g) + 2H2O(g) 3) Cu(s) + 2Ag+(g) Cu2+(g) + 2Ag(s) 4) H2(g) + I2(g) 2HI(g)
Tuesday, January 10, 2017 by Steve

Chemistry VERY DIFFICULT
Imagine you have been given a series of materials to react together and the following enthalpy change data has been recorded. Explain the terms exothermic and endothermic, and identify which of the following are exothermic and endothermic reactions. Ensure that you explain ...
Tuesday, January 10, 2017 by Jack

Chemistry
1. You have been given a sample of unknown molarity. Calculate the molarity of a solution which has been prepared by dissolving 8.75 moles of sodium chloride in enough water to produce a solution of 6.22l. 2. You have a sample which consists of 428g sodium hydroxide (NaOH) ...
Tuesday, January 10, 2017 by David

Science, Chemistry
A 1050.0 mL solution of NaOH is neutralized by 0.25 L of 2.00M Nitric Acid using Bromothymol Blue as an indicator. The concentration of the NaOH solution is 0.48M. True or False
Monday, January 9, 2017 by Anonymous

chemistry
Calculate the energy required for ionization of electron from the ground state of hydrogen atom
Monday, January 9, 2017 by donald

chemistry
Ammonia reacts with copper(ll)oxide to give nitrogen gas, copper and steam. Balance the equation. If 18.1g of ammonia is reacted with 90.4g of coope(ll)oxide,how many moles of each reacts?,and how many grams of nitrogen are formed?
Monday, January 9, 2017 by Juor

CHEMISTRY URGENT
1. You have been given a sample of unknown molarity. Calculate the molarity of a solution which has been prepared by dissolving 8.75 moles of sodium chloride in enough water to produce a solution of 6.22l. 2. You have a sample which consists of 428g sodium hydroxide (NaOH) ...
Monday, January 9, 2017 by Anonymous

chemistry help asap please
You have been given a sample of unknown molarity. Calculate the molarity of a solution which has been prepared by dissolving 8.75 moles of sodium chloride in enough water to produce a solution of 6.22l.
Monday, January 9, 2017 by David

CHEMISTRY
You have been given a sample of unknown molarity. Calculate the molarity of a solution which has been prepared by dissolving 8.75 moles of sodium chloride in enough water to produce a solution of 6.22l.
Monday, January 9, 2017 by Jason

Chemistry
CuCO3=CuO +CO2. Find the mass of 1mole of each substance taking part in the reaction. (Ar:Cu=64,C=12,O=16). When 31g of CuCO3 is used; 1)how many grams of CO2 is formed. 2) what mass of solid remains after heating.
Sunday, January 8, 2017 by Busola

Science Chemistry
LIST: SODIUM CARBONATE. CALCIUM CARBONATE. ZINC SULFATE. ZINC NITRATE. (a) State a pair of chemicals from the list above that can be used to prepare zinc carbonate by precipitation reaction involving mixing 2 aqueous solutions together. (b) Write a chemical equation for the ...
Saturday, January 7, 2017 by Charlotte

Science Chemistry
LIST: SODIUM CARBONATE. CALCIUM CARBONATE. ZINC SULFATE. ZINC NITRATE. (a) State a pair of chemicals from the list above that can be used to prepare zinc carbonate by precipitation reaction involving mixing 2 aqueous solutions together. (b) Write a chemical equation for the ...
Saturday, January 7, 2017 by Charlotte

Science Chemistry
LIST: Sodium carbonate. Calcium carbonate. Zinc sulfate. Zinc nitrate. (a) State a pair of chemicals from the list above that can be used to prepare zinc carbonate by a precipitation reaction involving mixing 2 aqueous solutions together. (b) Write a chemical equation reaction...
Saturday, January 7, 2017 by Charlotte

chemistry
Calculate the maximum number of unpaired electrons that can be placed in a 6d subshell
Saturday, January 7, 2017 by Donald

chemistry
2Na + 2H2O---> 2NaOH + H2 Need to find the molecules of H2 Atomic wt o Na = 23 48.7 g of Na 48.71/23 = 2.12 mols Na 2.12/2 × 24. (WHERE DOES THE 24 COME FROM) = 25.44 dm^3 H. (PLEASE EXPLAIN THIS PART) = 1.06moles 1.06mols× 6.02×10^23 avagados number= 1.204 × 10^24 ...
Saturday, January 7, 2017 by lulu

CHEMISTRY
A 70g sample of iron ore(Fe2O3) was analyzed for Iron and found to contain 1700 Fe. Calculate the percentage of iron in the sample.
Saturday, January 7, 2017 by JOSEPH BANDA

Chemistry
A 3 M HCL solution was used to generate the Co2 from the CaCO3. What would be the effect of substituting 6 M HCL for 3 M HCL? Explain
Friday, January 6, 2017 by Janie de rose

chemistry
writing blanced decomposition formula of Ammonium Carbonate
Thursday, January 5, 2017 by Hashini

Chemistry
Given the reaction below, and your knowledge of the "Law of Conservation of Mass", what is the missing product from the chemical reaction? How do you know? Zn(s) + HCl(aq) --> ___ + ZnCl2(aq)
Thursday, January 5, 2017 by Delaney

Chemistry
How many moles Of (Al2SO4)3 can be prepared from 2.5ml Of H2SO4
Thursday, January 5, 2017 by Dilna

AP Chemistry
Dinitrogen pentoxide (N2O5) decomposes in chloroform as a solvent to yield NO2 and O2. The decomposition is first order with a rate constant at 45 degrees Celsius of 1.0*10^-5 s^-1.Calculate the partial pressure of O2 produced from 1.00 Liter of 0.600 M N2O5 solution at 45 ...
Thursday, January 5, 2017 by Mckinley

Chemistry
Mean titre of 0.2M sodium thiosulphate = 32.2 ml 1) Calculate number of moles of S2O32- which react in the titration 2)Calculate how many moles of I2 react with this amount of S2O3 3)How many Cu2+ ions are needed to liberate this amount of I2? Use this answer as the number of ...
Thursday, January 5, 2017 by Chirag

chemistry
Calculatr morality of a solution containing 2.5g of K2CO3 in 1liter of solution (density of solution is 0.85 gram/ml
Thursday, January 5, 2017 by bilal

chemistry grade 11
ferrous sulfate was prepared by dissolution of x grams p feso4.7H20 crystals in 500 ml water. 20 ml of this solution necessities 5 ml of 0.1mol/l kmn04 for the pink color to persist. find x
Wednesday, January 4, 2017 by lana

chemistry
Write an equation for the reaction that take place in hydrogen sulphide gas when bubbled through a solution of zinc nitrate
Wednesday, January 4, 2017 by kennedy

chemistry
What would be made if hydrogen sulphide gas was bubbled through a solution of zinc nitrate
Wednesday, January 4, 2017 by kennedy

Chemistry
calculate number of moles of NH3 if 8g of H2 reacts in excess N2
Tuesday, January 3, 2017 by Zohaib

Chemistry
NaCl [Symbol] Na + Cl2 Type of reaction: synthesis KOH + HNO3 [Symbol] HOH + KNO3 Type of reaction: double replacement Ca + S [Symbol] CaS Type of reaction: synthesis BaBr2 + Cl2 [Symbol] BaCl2 + Br2 Type of reaction: Cs2 + H2O [Symbol] CsOH + H2 Type of reaction: Na2CO [...
Tuesday, January 3, 2017 by Chemistry

Chemistry
How many molecules present in 500ml of 42g NaHCO3?
Tuesday, January 3, 2017 by CBEMISTRYISLIFE

chemistry
How is sulphur manufactured in a large scale
Tuesday, January 3, 2017 by jayce

Chemistry HELP! CONFUSED!
How do you do this? please help. Thank you. A.) Suppose 2.5 grams of sodium hydrogen carbonate reacts with acetic acid, calculate how many liters of carbon dioxide gas will be produced at 22 degrees celcius and 1.10 atm. B.) Suppose 0.990 liters of carbon dioxide at 25 degrees...
Monday, January 2, 2017 by Julia B

Chemistry
Hello, Is there a reaction when NaNO3 is added to some H2O? Or does it just dissolves? Please explain why, thanks!
Monday, January 2, 2017 by Sherlique

Chemistry
If I add water to NaNO3 does it make HNO3 and NaOH? For example NaNO3 + H2O -> HNO3 + NaOH is that equation correct? Please explain if it's not. Thanks!
Monday, January 2, 2017 by Sherlique

chemistry
Hello, Is nano3 + h2o -> naoh + hno3 correct?
Sunday, January 1, 2017 by Sherlique

chemistry
Name two metals which are obtained by reducing thier oxides by heating with aluminium How is the metal oxides present in calcined/roasted ore reduced to the metal
Sunday, January 1, 2017 by Anonymous

chemistry
Name two metals which are obtained by reducing thier oxides by heating with aluminium How is the metal oxides present in calcined/roasted ore reduced to the metal
Sunday, January 1, 2017 by Anonymous

Chemistry
Is this a valid equation? NaNO3 + H2O = NaOH + HNO3 Why or why not?
Sunday, January 1, 2017 by Sherlique

chemistry AS
how do you draw the skeletal structure for (z)-pent-2-ene.
Saturday, December 31, 2016 by hifza

Chemistry
Hello, If I add water to a solid, how do i represent it in a equation with phases? for example the NaNO3 was the solid in this case and H2O was the liquid, does NaNO3 turns into an aqueous or stays as solid when I write the equation? Which one would be correct? 1) NaNO3(s) + ...
Saturday, December 31, 2016 by Sherlique

Chemistry
Using equation only. Show how tetraoxosulphate(IV) can be prepared industrially
Saturday, December 31, 2016 by UMEADI

Chemistry
Hello, Which one is correct? 1) NaOH(aq) + HNO3(aq) ⇋ NaNO3(aq) + H2O(l) or 2) NaNO3(s) + H2O(l) ⇋ NaOH(aq) + HNO3(aq) Thanks!!
Saturday, December 31, 2016 by Sherlique

Chemistry
Iron+CON Hydrochloric acid =?
Saturday, December 31, 2016 by Anonymous

Chemistry
Hello, Sorry to bother you all, but i have a quick question. If I needed to use heat in a reaction, for example, Ca(OH)2(s) + 2NH4Cl(s) = 2H2O(g) + 2NH3(g) + CaCl2(s) Do I need to put "+heat" on the reactant side when writing my equation? Thanks in advance! :)
Saturday, December 31, 2016 by Sherlique

chemistry
a sample of gaseous substance at 25 degrees Celsius and 0.862atm has a density of 2.6g/l. what is the molecular weight of the substance?
Friday, December 30, 2016 by Goodness

chemistry
if 3.15g of mercury are thermally decomposed to mercury and oxygen what mass of mercury will be produced and how many oxygen molecules will be produced [hg=208,o=16]
Friday, December 30, 2016 by jj

Chemistry
Hello, 1) What is the PH if ammonia is mixed with water vapour? 2) What is the white smoke when I heat NH4Cl with Ca(OH)2? Thanks
Thursday, December 29, 2016 by Sherlique

Chemistry
Hello, What are the phases for this equation? NaNO3 + H2O ⇋ NaOH + HNO3 Oh and can I write the equation this way as well? NaOH + HNO3 ⇋ NaNO3 + H2O Do they mean the same thing?
Thursday, December 29, 2016 by Sherlique

Chemistry
One mole of an ideal gas is allowed to expand isothermally at -29. 3degrees celcious from a volume of 4. 0L and apressure of 5. 0atm to avolume of 10. 0L and apressure of 2. 0atm. i. Draw a p-v diagram for the process. ii. Determine the work done by the fasduring expansion.
Thursday, December 29, 2016 by Patrick

Chemistry
Hi, what is the PH for NH3 in gas form? When I tested it with PH paper it showed a number around 8-9.5, but from searching online its a higher number. I'm not sure which one is correct. Thanks
Thursday, December 29, 2016 by Sherlique

chemistry
Hi, I was wondering why is there white smoke when nh4cl and ca(oh)2 is being heated. Thanks!
Thursday, December 29, 2016 by Sherlique

Chemistry
1. A student collected the following data for a fixed volume of gas: Temperature (⁰C) Pressure (mm of Hg) 10 726 20 750 40 800 70 880 100 960 150 ??? Fill in the missing data point. Show all calculations leading to an answer.
Wednesday, December 28, 2016 by sophia

Chemistry
Which of the following is true about oxidation reactions? A. Oxidation reactions are the principal source of energy on Earth. B. All oxidation reactions are accompanied by reduction reactions. C. The burning of wood in a fireplace and the metabolization of food by your body ...
Wednesday, December 28, 2016 by sophia

SAT Math
All of the students who took chemistry at Groveton High School last year were juniors or seniors, as shown in the table below. If 80% of the students who took chemistry passed, then what fraction of the students in the combined junior and senior classes took chemistry? Class ...
Tuesday, December 27, 2016 by Kay

Chemistry AP
How many mL of0.4M AgNO3 solution must be added to 200mL of0.4 M NaI in order to for 11.7 grams of AgI precipitate?
Tuesday, December 27, 2016 by Angel

  1. Pages:
  2. <<Prev
  3. 1
  4. 2
  5. 3
  6. 4
  7. 5
  8. 6
  9. 7
  10. 8
  11. 9
  12. 10
  13. 11
  14. 12
  15. 13
  16. 14
  17. 15
  18. Next>>

Homework Help: Science