Discussion
149 g of \(KCl\) is dissolved in 10 litres of an aqueous solution. The molarity of the solution is (molar mass of \(KCl\) = 74.5)
Answer: D
The molarity is 0.2M.
Molarity is moles of solute per litre of solution:
\[ \begin{aligned} n &= \frac{149}{74.5} = 2\ \text{mol} \\ M &= \frac{2\ \text{mol}}{10\ \text{L}} = 0.2\ \text{M} \end{aligned} \]
2 M forgets to divide by the 10 litres, and 0.002 M divides by a further 100. 0.1M takes the solute as 1 mol instead of 2, and 1M makes both mistakes at once.
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