\(0 \cdot 15 \mathrm{M}\) solution means than \(0.15\) mole of benzoic acid is dissolved in \(1 \mathrm{~L}\) of solution.
Molar mass of \(\mathrm{C}_6 \mathrm{H}_5 \mathrm{COOH}\)
\(\begin{aligned}=12 \times 6+5+12+2 \times 16+1=122 \mathrm{~g} \mathrm{~mol}^{-1} \\ \text { Mass of } 0.15 \text { mole of } \mathrm{C}_6 \mathrm{H}_5 \mathrm{COOH} &=0 \cdot 15 \times 122 \\ &=18 \cdot 3 \mathrm{~g} \end{aligned}\)
Thus, \(1 \mathrm{~L}\) or \(1000 \mathrm{~mL}\) of solution contain
\(=18 \cdot 3 \mathrm{~g} \mathrm{ofC}_6 \mathrm{H}_5 \mathrm{COOH}\)
\(\therefore 250 \mathrm{~mL}\) of the solution will contain
\(=\frac{18 \cdot 3}{1000} \times 250=4 \cdot 575 \mathrm{~g} \mathrm{of}_6 \mathrm{H}_5 \mathrm{COOH}\).