Answer: 8.59 L of oxygen gas are needed to produce 100 kJ of energy at STP
Explanation:
According to avogadro's law, 1 mole of every substance occupies 22.4 L at STP and contains avogadro's number 
of particles.
Standard condition of temperature (STP) is 273 K and atmospheric pressure is 1 atmosphere respectively.
1 mole of every gas occupy volume at STP = 22.4 L
The balanced chemical reaction is:
3909.9 kJ of of energy is produced by = 
100 kJ of oxygen gas are needed to produce = 
3Mg + N₂= Mg₃N₂
n(Mg)=12,2g÷<span>24,4g/mol=0,5mol-limiting reagent
</span>n(N₂)=5,16g÷28g/mol=0,18mol
n(Mg₃N₂):n(Mg)=1:3, n(Mg₃N₂)=0,166mol, m(Mg₃N₂)=0,166·101,2=16,8g.
%(N)= 2·Ar(N)÷Mr(Mg₃N₂) = 2·14÷101,2=27,66%=0,2766
%(Mg) = 3·Ar(Mg)÷Mr(Mg₃N₂)= 3·24,4÷101,2=72,34% or 100% - 27,66%= 72,34%.
The reaction is not balanced
<h3>Further explanation</h3>
Given
Reaction
2Fe(s)+3O₂(g)⇒2Fe₂O₃(s)
Required
The number of atoms
Solution
In a balanced chemical equation, the number of atoms in the compound that reacts (the reactants and products) will have the same number
Reactants : Fe(s)+O₂(g)
Fe = 2 atoms
O = 3 x 2 = 6 atoms
Products : Fe₂O₃(s)
Fe = 2 x 2 = 4 atoms
O = 2 x 3 = 6 atoms
The reaction is not balanced because the number of Fe atoms is not the same
The balanced reaction should be:
4Fe(s)+3O₂(g)⇒2Fe₂O₃(s)
I belive its D if not right sorry.
