Identify the correct statements: (A) The molality of 2.5 g of ethanoic acid (Molar mass: $60{\text{g mol}}^{-1}$) in 75 g of benzene solution is 0.556 m. (B) The molarity of a solution containing 5 g of $\mathrm{NaOH}$ (molar mass: $40{\text{g mol}}^{-1}$) in 450 mL of solution is 0.278 M at 298 K. (C) Aquatic species are more comfortable in cold water. (D) The solubility of a gas increases with decrease in pressure. (E) For a binary mixture of A and B, the number of moles of A and B are $n_A$ and $n_B$ respectively. The mole fraction of B will be $x_B=\frac{n_A}{n_A+n_B}$.

Solution & Explanation

\textbf{Answer:} (A) A, B and C only \textbf{Solution:} (A) Molality $=\frac{2.5/60}{75/1000}=\frac{0.0417}{0.075}=0.556m$ — correct. (B) Molarity $=\frac{5/40}{450/1000}=\frac{0.125}{0.45}=0.278M$ — correct. (C) Gas solubility increases as temperature falls, so cold water holds more dissolved $\mathrm{O}{}_2$; aquatic species are more comfortable in cold water — correct. (D) Solubility of a gas \textbf{increases with increase} in pressure (Henry's law), not with a decrease — FALSE. (E) The expression $\frac{n_A}{n_A+n_B}$ is actually $x_A$, not $x_B$ — FALSE. Correct statements: A, B and C → option (A).