KHCO₃ is contaminated with K₂CO₃ as impurity. If 2.5g of the impure KHCO₃ on heating produces 0.224dm³ of CO₂ at s.t.p., calculate the percentage of K₂CO₃ impurity
(K = 39, H = 1, C = 12, O = 16)

• A.30%
• B.40%
• C.10%
• D.20%