The given question is incomplete. The complete question is:
How much heat is produced when 24.8 g of 
is burned in excess oxygen gas
Given: 
ΔH= −802 kJ.
Answer: 1243.1 kJ
Explanation:
Heat of combustion is the amount of heat released on complete combustion of 1 mole of substance.
Given :
Amount of heat released on combustion of 1 mole of methane = 802 kJ kJ/mol
According to avogadro's law, 1 mole of every substance occupies 22.4 L at NTP, weighs equal to the molecular mass and contains avogadro's number 
of particles.
1 mole of weighs = 16 g
Thus we can say:
16 g of on combustion releases heat = 802 kJ
Thus 24.8 g of on combustion releases =
Thus heat released when 24.8 g of methane is burned in excess oxygen gas is 1243.1 kJ
The volume of O₂ produced: 84.6 L
<h3>Further explanation</h3>
Given
7.93 mol of dinitrogen pentoxide
T = 48 + 273 = 321 K
P = 125 kPa = 1,23365 atm
Required
Volume of O₂
Solution
Decomposition reaction of dinitrogen pentoxide
2N₂O₅(g)→4NO₂(g)+O₂ (g)
From the equation, mol ratio N₂O₅ : O₂ = 2 : 1, so mol O₂ :
= 0.5 x mol N₂O₅
= 0.5 x 7.93
= 3.965 moles
The volume of O₂ :
The third option because the elements mentioned in that selection are in the same group, they must have similar properties.
