Data inconsistency prevents calculating K Steps:

• The reaction is PCl₅ ⇌ PCl₃ + Cl₂; initial moles of PCl₅ = 1 in 1 dm³.
• At equilibrium, moles of PCl₅ should be less than 1 due to dissociation.
• Given 1.8 mol PCl₅ at equilibrium contradicts the reaction stoichiometry, as moles cannot increase.
• Not enough information to compute Kc = [PCl₃][Cl₂]/[PCl₅].

Why B is correct:

• Not applicable; no valid K can be determined.

Why the others are wrong:

• A: No basis for K=1 without valid equilibrium data.
• C: No basis for K=9 without valid equilibrium data.
• D: No basis for K=16.2 without valid equilibrium data.

Final answer: Not enough information.