Balance each of the following skeleton equations.

C) C3H8 + O2 -> CO2 + H2O

This one was a bit harder for me to balance out, but this is what I managed to do.

C3H8 + O2 -> 3CO2 + 8H

C3H8 + O2 -> 3CO2 + 8H

Nope. You never need to guess if you balanced an equation or not. Just check it.
I see 3C on both sides. Good.
I see 2 O on the left and 7 on the right. nope.
I see 8 H on the left and 8 on the right BUT that should be 4H2 and not 8H.

C3H8 + 5O2 ==> 3CO2 + 4H2O

To balance the given equation C3H8 + O2 -> CO2 + H2O, start by counting the number of atoms on each side of the equation.

C3H8: 3 carbon (C) atoms, 8 hydrogen (H) atoms
O2: 2 oxygen (O) atoms
CO2: 1 carbon (C) atom, 2 oxygen (O) atoms
H2O: 2 hydrogen (H) atoms, 1 oxygen (O) atom

Since there are 3 carbons on the left side and only 1 carbon on the right side, balance the carbons by putting a coefficient of 3 in front of the CO2:

C3H8 + O2 -> 3CO2 + H2O

Next, balance the hydrogen atoms. There are 8 hydrogen atoms on the left side and only 2 hydrogen atoms on the right side. Put a coefficient of 4 in front of the H2O to balance the hydrogens:

C3H8 + O2 -> 3CO2 + 4H2O

Finally, balance the oxygen atoms. There are 2 oxygen atoms in O2 and 4 oxygen atoms in 4H2O, which gives a total of 10 oxygen atoms on the right side. To balance this, put a coefficient of 5/2 (or 2.5) in front of O2:

C3H8 + 5/2O2 -> 3CO2 + 4H2O

However, it is best to avoid using fractional coefficients. To eliminate the fractional coefficient, multiply the entire equation by 2 to get rid of the fraction:

2 C3H8 + 5 O2 -> 6 CO2 + 8 H2O

Therefore, the balanced equation is:

2 C3H8 + 5 O2 -> 6 CO2 + 8 H2O