Hess's law cannot be applied directly

Steps:

• The target reaction K₂CO₃(s) + H₂O(l) → 2KHCO₃(s) is not atomically balanced (1 C and 4 O on left vs. 2 C and 6 O on right).
• The given reactions both produce CO₂(g), which is absent in the target.
• Combining them via Hess's law yields K₂CO₃(s) + H₂O(l) + CO₂(g) → 2KHCO₃(s) with ΔH = -34 + 2(32) = +30 kJ mol⁻¹.
• Without data to account for the missing CO₂ or unbalanced atoms, the target's ΔH cannot be determined.

Why D is correct:

• D provides a positive value consistent with the endothermic nature of the balanced analog, but the question's imbalance makes all options invalid.

Why the others are wrong:

• A is nearly the second reaction's ΔH, irrelevant here.
• B and C are arbitrary sums/differences not matching any valid combination.

Not enough information.

Final answer: Not enough information.