The plains from Ambala to the Sunderban stretch over nearly 1800 km, but the fall in its slope is hardly _____ metres.

300

The correct answer is Option (2) - 300

The clue lies in the statement itself. It mentions that the plains stretch over nearly 1800 km but the fall in slope is hardly any. This suggests a very minimal change in elevation over a long distance.

• 550, 600, 450 meters: These values are relatively high for a "hardly" significant change in slope over 1800 km.
• 300 meters: This value indicates a small change in elevation, making it the most likely answer for a "hardly" noticeable slope.