Question:
Assertion (A): Molality of solution increases with temperature.
Reason (R): Molality expression does not involve any volume term.
Assertion (A): Molality of solution increases with temperature.
Reason (R): Molality expression does not involve any volume term.
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Molality depends on mass, while molarity depends on volume. Since volume changes with temperature but mass does not, molarity changes with temperature whereas molality remains constant.
Updated On: Jun 18, 2026
- Both A and R are correct, R is the correct explanation of A.
- Both A and R are correct, R is not the correct explanation of A.
- A is correct, R is not correct.
- A is not correct, R is correct.
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The Correct Option is D
Solution and Explanation
Step 1: Examine the assertion.
Molality is defined as \[ m=\frac{\text{moles of solute}}{\text{mass of solvent (kg)}} \] Since both moles of solute and mass of solvent remain unchanged with temperature, molality remains constant.
Therefore, the statement \[ \text{“Molality increases with temperature”} \] is incorrect.
Hence, Assertion (A) is false.
Step 2: Examine the reason.
The expression for molality is \[ m=\frac{\text{moles of solute}}{\text{mass of solvent}} \] No volume term appears in this expression.
Since mass is independent of temperature, molality is also independent of temperature.
Therefore, Reason (R) is correct.
Step 3: Final conclusion.
Assertion (A) is false, whereas Reason (R) is true.
Hence, \[ \boxed{\text{A is not correct, R is correct}} \] Therefore, the correct option is (4).
Molality is defined as \[ m=\frac{\text{moles of solute}}{\text{mass of solvent (kg)}} \] Since both moles of solute and mass of solvent remain unchanged with temperature, molality remains constant.
Therefore, the statement \[ \text{“Molality increases with temperature”} \] is incorrect.
Hence, Assertion (A) is false.
Step 2: Examine the reason.
The expression for molality is \[ m=\frac{\text{moles of solute}}{\text{mass of solvent}} \] No volume term appears in this expression.
Since mass is independent of temperature, molality is also independent of temperature.
Therefore, Reason (R) is correct.
Step 3: Final conclusion.
Assertion (A) is false, whereas Reason (R) is true.
Hence, \[ \boxed{\text{A is not correct, R is correct}} \] Therefore, the correct option is (4).
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