Explanation: \(\text{Hints: } f_2 - f_1 = 250; \, v = f\lambda\) \(\text{Solve: } f_2 - f_1 = 250 \implies v\left(\frac{1}{\lambda_2} - \frac{1}{\lambda_1}\right) = 250 \implies v\left(\frac{1}{2} - \frac{1}{2.5}\right) = 250\) \(\implies v \times 0.1 = 250 \implies v = \frac{250}{0.1} \therefore v = 2500 \, \text{m/s}\) \(\text{Ans. (C)}\)