I can answer (a) and (d)
For a:-
The candle flame went out due to lack of O2 gas.Oxygen gas is very inportant for combustion process.
General equation for combustion is
CH4 + 2O2 → CO2 + 2H2O
For d:-
The air is made of following major elements
1 nitrogen 78%
2 Oxygen 21%
3 Argon. 0.93% almost 1%
