Question

Identify the correct statements. A. Molality of a solution is defined as mass of solute in gram dissolved in solution.
B. Molality of a solution is defined as the number of moles of solute dissolved in \(1\text{ kg}\) of solvent.
C. Aqueous solution of \(\ce{NH4OH}\) and \(\ce{NH4Cl}\) is a basic buffer solution.
D. Solubility of a gas in a liquid increases with increase in pressure.

• A. A and B only
• B. B, C and D only
• C. A, B and C only
• D. A and C only

Hint:

Molality is moles of solute per kg of solvent. A weak base and its salt form a basic buffer.

Answer 1

The Correct Option is B

Step 1: Check statement A.
Statement A says molality is mass of solute in gram dissolved in solution. This is incorrect. Mass of solute in gram alone does not define molality. Molality depends on: \[ \text{moles of solute} \] and: \[ \text{mass of solvent in kg}. \] So statement A is incorrect.

Step 2: Check statement B.
Molality is defined as: \[ m=\frac{\text{moles of solute}}{\text{mass of solvent in kg}} \] So statement B is correct.

Step 3: Check statement C.
A basic buffer is formed by a weak base and its salt with a strong acid. Here: \[ \ce{NH4OH} \] is a weak base. \[ \ce{NH4Cl} \] is its salt with strong acid \(\ce{HCl}\). Therefore: \[ \ce{NH4OH + NH4Cl} \] forms a basic buffer. So statement C is correct.

Step 4: Check statement D.
According to Henry's law, the solubility of a gas in liquid increases with increase in pressure at constant temperature. So statement D is correct.

Step 5: Final conclusion.
The correct statements are: \[ B,\ C,\ D. \] Therefore, the correct answer is: \[ \text{B, C and D only}. \]