Out of \(18 g\) of glucose only \(4.5 g\) is dissolved in water to obtain \(40 mL\) of its aqueous solution. Find the molarity of this glucose solution
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 0.625 M
Molarity is the number of moles of solute dissolved in one litre of solution:
\( \displaystyle M = \frac{\text{moles of solute}}{\text{volume of solution in L}} \)
Only the glucose that is dissolved counts, i.e. 4.5 g (the undissolved part of the 18 g is not in the solution). Molar mass of glucose, \( \ce{C6H12O6} \) = 180 g mol−1.
\( \displaystyle n = \frac{4.5\ \text{g}}{180\ \text{g mol}^{-1}} = 0.025\ \text{mol} \)
\( \displaystyle M = \frac{0.025\ \text{mol}}{0.040\ \text{L}} = \mathbf{0.625\ M} \)
NCERT (2026-27 edition):
Expressing Concentration of Solutions – …
