Which solution contains the biggest amount, in mol, of chloride ions?

A.     \({\text{20 c}}{{\text{m}}^{\text{3}}}\) of \({\text{0.50 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}{\text{N}}{{\text{H}}_{\text{4}}}{\text{Cl}}\)

B.     \({\text{60 c}}{{\text{m}}^{\text{3}}}\) of \({\text{0.20 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}{\text{MgC}}{{\text{l}}_{\text{2}}}\)

C.     \({\text{70 c}}{{\text{m}}^{\text{3}}}\) of \({\text{0.30 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}{\text{NaCl}}\)

D.     \({\text{100 c}}{{\text{m}}^{\text{3}}}\) of \({\text{0.30 mol}}\,{\text{d}}{{\text{m}}^{ - 3}}{\text{ClC}}{{\text{H}}_{\text{2}}}{\text{COOH}}\)

B

Students found this question one of the more difficult ones, with only 28.15% correct answers. Most candidates answered D, a molecular compound which would have no chloride ions present (the other three were ionic). Students had to address the question of ionic versus molecular structure, which was straight forward as well as the quantitative aspect.