7.102 g of ${\text{N}}{{\text{a}}_2}{\text{S}}{{\text{O}}_4}{\text{ (}}M = 142.04{\text{ g}}\,{\text{mo}}{{\text{l}}^{ - 1}}{\text{)}}$ is dissolved in water to prepare ${\text{0.5000 d}}{{\text{m}}^{\text{3}}}$ of solution. What is the concentration of ${\text{N}}{{\text{a}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}$ in ${\text{mol}}\,{\text{d}}{{\text{m}}^{ - 3}}$?

A.     $2.500 \times {10^{ - 2}}$

B.     $1.000 \times {10^{ - 1}}$

C.     $1.000 \times 10$

D.     $1.000 \times {10^2}$

B

There was some concern that, for the mathematically challenged, the figures given were too difficult. Although it could perhaps have been simplified to 7.1 g and ${\text{142 g}}\,{\text{mo}}{{\text{l}}^{ - 1}}$ nearly 57% of candidates gave the correct answer, the next most common being A (nearly 25%) which showed an incorrect concentration calculation.