600 metres
Explanation
Landforms are primarily classified into mountains, plateaus, and plains based on elevation, slope, and relief. The distinction between a hill and a mountain is a specific convention based on vertical height above mean sea level.Detailed Analysis:
- 600 metres is Correct: According to standard geographical conventions, a natural elevation of the earth's surface rising more than 600 metres with a steep slope is designated as a mountain. Elevations lower than this threshold are typically classified as hills.
- Options 200 metres, 400 metres, and 800 metres are Incorrect: These values do not represent the standard threshold for distinguishing mountains from hills. While definitions vary globally (e.g., the UK and US have used different metrics historically), the 600-metre benchmark is the specific figure used in the context of this classification within Indian academic geography.
Key Takeaway: The standard elevation threshold distinguishing a mountain from a hill is 600 metres; landforms exceeding this height with steep slopes are termed mountains.