Consider a potentiometer set-up where a cell of emf 2.25 V gives a balance point at 63.0 cm length of the wire. Now the cell is replaced by another cell and the balance point shifts to 21.0 cm. Then the emf of the second cell is:

Correct option is A

​$$\text{1. Balanced condition for potentiometer:} \\\text{The potentiometer provides a balanced condition that can be written as:} \\\frac{E_1}{E_2} = \frac{l_1}{l_2} \\\\\text{2. Rearranging for } E_2: \\E_2 = E_1 \times \frac{l_2}{l_1} \\\\\text{3. Substituting the given values:} \\E_2 = 2.25 \times \frac{21.0}{63.0} \\\\\text{4. Simplifying the expression:} \\E_2 = 2.25 \times \frac{21}{63} = 0.75 \, \text{V}$$​​