The correct option is D Heat at constant pressure is a state function
A) pressure and volume are state functions and hence their product must be state function.
B) According to the first law of thermodynamics
ΔU=Δq+W
For an adiabatic process Δq=0. Thus W=ΔU. Since U is a state function, hence work done under adiabatic condition is a state function.
C) We know, ΔU=Δq+PΔV.
So at constant volume Δq=ΔU, hence heat at constant volume is a state function.
D) Heat at constant pressure is equal to ΔH. So Heat at constant pressure is a state function