Multiple choice...thanks for helping...?

Question

1. The complete combustion of octane (C8H18) in a car engine is best described by the equation
a) C8H18(g) + O2(g) -(arrow) CO2(g) + H2O(g)
b) C8H18(g) + 17O2(g) -(arrow) 8CO2(g) + 18H2O(g)
c) 2C8H18(g) + 34O2(g)-(arrow) 16CO2(g) + 18H2O(g)
d) 2C8H18(g) + 25O2(g) -(arrow) 16CO2(g) + 18H2O(g)

2. Natural gas which is used for domestic heating, burns according to the equation CH4(g)+2O2(g) - (arrow) CO2(g) + 2H2O(g)
In this process, if complete raction occurs,
a) 16g of methane produces 18g of water
b) 1g of methane produces 12g of carbon dioxide
c) 1g of methane reacts with 4g of oxygen
d) 4g of methane reacts with 8g of oxygen

3. If equal masses of each of the followign are burned in excess oxygen, which will give the greatest mass of CO2?
a) CH4
b) CH3OH
c) C2H2
d) CH3CH2OH

Thankyou. Please help Chemistry wizzes! Please be 100% sure of your answers. Thanks.

Answer 1

1.) The key is "best described". The octane is probably not entirely a gas, but a mixture or liquid droplets and vapor. Their would probably be some CO as well as CO2 for the combustion of the carbon. The answer is d.

2.) Looking at the equation, the grams (calculated from the number of moles) is:
16 g of CH4 + 64 g of O2 --> 44 g of CO2 + 36 g of H2O
The answer is c.

3.) The MM's are (followed by the fraction of Carbon):
CH4 = 16 (12/16)
CH3OH = 32 (12/32)
C2H2 = 26 (24/26)
CH3CH2OH = 46 (24/46)
The answer is c (ethyne or acetylene).

Answer 2

Question 1: The correct answer is (d) as it is the only one of the equations which is correctly balanced.

Question 2: (c) would be true. 1 gram of methane is 1/16 of a mole. So you would need 2/16 of a mole of O2 (as you need two moles according to the balanced equation). 2/16 of a mole of O2 is 4 grams. So (c) is true.

Question 3: The correct answer will be the one that has the highest mass percent of carbon. So, anything with oxygen will be excluded as it is heavy. CH4 is 75% carbon by mass while C2H2 is 92%. So the correct answer would be (c)