Question

a Colony of mountains surrounded the valley . correct the incorrect use of collective noun​

Answer 1

I think it should be range instead of colony.

group of mountains is called range.

Answer 2

Answer:

The valley is surrounded by mountain range.

Or  

A range of mountains surrounds the valley.

Explanation:

Collective nouns are used to define the group of names or people or object. Collective nouns are plural or singular and it may depends on the context or things and it refers to multiple people or things.

When we use collective nouns for “mountains” we often say “mountain range”. The meaning of the sentence is “mountains” which is a group of mountains and it surrounds the “valley”.