A liquid possessing which of the following characteristics will be most suitable for determining the molecular mass of a compound by cryoscopic measurements ?

Options

A. That having low freezing point and small enthalpy of freezing
B. That low high freezing point and small enthalpy of freezing
C. That having high freezing point and small enthalpy of vapourisation
D. That having large surface tension

Explanation

To determine the molecular mass of a compound using cryoscopic measurements, we need to consider the characteristics of the liquid used in the process. Here’s a step-by-step solution to the question:

### Step 1: Understand Cryoscopic Measurements
Cryoscopic measurements involve determining the change in freezing point (ΔTf) of a solvent when a solute is added. The relationship is given by the formula:
\[ \Delta T_f = K_f \times m \times i \]
where:
- \( \Delta T_f \) = change in freezing point
- \( K_f \) = cryoscopic constant of the solvent
- \( m \) = molality of the solution
- \( i \) = van't Hoff factor (which accounts for the number of particles the solute dissociates into)

### Step 2: Identify Key Factors
From the formula, we see that the cryoscopic constant \( K_f \) plays a crucial role in determining the extent of the freezing point depression. A higher \( K_f \) value will lead to a more significant change in freezing point for a given amount of solute.

### Step 3: Characteristics of the Liquid
To maximize \( K_f \), we need:
- A **high freezing point** (Tf) because \( K_f \) is directly proportional to Tf.
- A **low enthalpy of fusion** (ΔHf) because \( K_f \) is inversely proportional to ΔHf.

### Step 4: Conclusion
Thus, the most suitable liquid for cryoscopic measurements will be one that has:
- A **high freezing point** (to ensure a larger \( K_f \))
- A **low enthalpy of fusion** (to maximize \( K_f \))

### Final Answer
The liquid possessing a **high freezing point and low enthalpy of fusion** will be most suitable for determining the molecular mass of a compound by cryoscopic measurements.

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