The correct option is A −7.42 kJ
We know,
Heat of a reaction at constant pressure = ΔH
Heat of reaction at constant volume = ΔU
Again,
ΔH=ΔU+PΔV
⇒ΔH=ΔU+ΔngRT
⇒ΔH−ΔU=ΔngRT
T=25∘C or 298 K
For the reactipon :
A(g)+3B(g)→C(g)
Δng=nP−nR
=1−4
=−3
On substituting the values;
ΔH−ΔU=(−3)(8.3)×298
=−7420.2 J
=7.42 kJ