The correct option is B −12.140 Kcal
The van't Hoff equation is logK2K1=+ΔH2.303R[1T1−1T2]=ΔH2.303R[T2−T1T1T2].
Here, K1 and K2 are the values of the equilibrium constants at temperatures T1 and T2 respectively.
ΔH is the enthalpy of the reaction and R is the ideal gas constant.
Substitute values in the above expression.
2.303 log(0.01290.0266)=ΔH2[673−623673×623]ΔH=−12140 cal=−12.140 kcal.