Answer :
The volume of H₂ evolved at NTP=0.336 L
Further explanation
Reaction
Decomposition of NH₃
2NH₃ ⇒ N₂ + 3H₂
conservation mass : mass reactants=mass product
0.28 NH₃= 0.25 N₂ + 0.03 H₂
2 g H₂ = 22.4 L
so for 0.03 g :
[tex]\tt \dfrac{0.03}{2}\times 22.4=0.336[/tex]