Explanation:

- The train is 750 meters long.

- It crosses a stationary pole in 15 seconds.

- The speed of the train is calculated as the distance divided by time: \( \text{Speed} = \frac{750}{15} = 50 \) meters per second.

- The train crosses a bridge completely in 25 seconds.

- The length of the bridge plus the length of the train is the distance covered in 25 seconds: \( \text{Distance} = \text{Speed} \times \text{Time} = 50 \times 25 = 1250 \) meters.

- The length of the bridge is \( 1250 - 750 = 500 \) meters.

- Correct Option: Option 4 - 500