At STP 4 liters of O2 contains the same total number of molecules as 4 L of CO2? is that right?

OR

8 L of HE, 1 L of NH3

Well the answer is definitely correct because that is the one selected on the answer sheet. I don't know why though.

To determine whether 4 liters of O2 contains the same total number of molecules as 4 liters of CO2, we need to compare the number of molecules present in each gas at standard temperature and pressure (STP).

At STP, the temperature is 273.15 Kelvin and the pressure is 1 atmosphere. We can use the ideal gas law equation, which states that PV = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the ideal gas constant, and T is the temperature.

First, let's calculate the number of moles of O2 in 4 liters. Since the volume is given in liters, we don't need to convert it.

Using the ideal gas law, we have:
PV = nRT
(1 atm) * (4 L) = n * (0.0821 L·atm/mol·K) * (273.15 K)

Simplifying the equation, we find:
4 atm·L = n * 22.414 L·atm/mol

Dividing both sides by 22.414 L·atm/mol, we have:
n = 4 atm·L / 22.414 L·atm/mol

Calculating this gives us:
n ≈ 0.178 moles

Next, let's calculate the number of moles of CO2 in 4 liters. Again, we'll use the ideal gas law:

PV = nRT
(1 atm) * (4 L) = n * (0.0821 L·atm/mol·K) * (273.15 K)

Simplifying the equation, we get:
4 atm·L = n * 22.414 L·atm/mol

Dividing both sides by 22.414 L·atm/mol, we have:
n = 4 atm·L / 22.414 L·atm/mol

Calculating this gives us:
n ≈ 0.178 moles

Therefore, we find that 4 liters of O2 and 4 liters of CO2 contain the same total number of molecules since they both have approximately 0.178 moles at STP.

Regarding the second part of your question, to determine whether 8 liters of He contains the same total number of molecules as 1 liter of NH3, we would need to follow a similar process. However, we need the molar mass of the gases to calculate the number of moles. Please provide the molar masses of He and NH3 so that we can proceed with the calculation.