Class 12 NEET Chemistry Solutions Questions

Concept:Molality, molarity, Henry’s law for gas solubility, and mole fraction in a binary mixture are evaluated.Chemical Equation / Formula:Molality $= \frac{\text{moles of solute}}{\text{mass of solvent (kg)}}$Molarity $= \frac{\text{moles of solute}}{\text{volume of solution (L)}}$Henry’s law: $P = K_H x$ (solubility $\propto$ pressure)Mole fraction of B: $x_B = \frac{n_B}{n_A + n_B}$Explanation:(A) Moles of ethanoic acid $= \frac{2.5}{60} = 0.04167$Mass of benzene $= 75\ \text{g} = 0.075\ \text{kg}$Molality $= \frac{0.04167}{0.075} = 0.556\ \text{molal}$Thus statement (A) is correct.(B) Moles of NaOH $= \frac{5}{40} = 0.125$Volume $= 450\ \text{mL} = 0.45\ \text{L}$Molarity $= \frac{0.125}{0.45} = 0.278\ \text{M}$Thus statement (B) is correct.(C) Cold water has lower temperature. Gas solubility increases as temperature decreases (Henry’s law).So aquatic species find cold water more comfortable due to higher dissolved oxygen.Thus statement (C) is correct.(D) According to Henry’s law, solubility $\propto$ pressure. So solubility decreases when pressure decreases is false.Thus statement (D) is incorrect.(E) Mole fraction of B should be $x_B = \frac{n_B}{n_A + n_B}$, not $\frac{n_A}{n_A + n_B}$.Thus statement (E) is incorrect.Answer:Correct statements: A, B and C only → Option A.