A Range … like the Alps Mountain Range
The collective nouns for mountains are a chain of mountains or a range of mountains.
cordillera
A group of mountains is commonly referred to as a range or a mountain range.
That would be the Himalayan chain of mountains.
A group of many mountains is called a mountain range or a mountain chain.
You may be thinking of the Trans-Antarctic mountains.
A string of mountains is called a mountain chain.
Appalachian Mountains (oldest in US)
Mid-Atlantic chain
The longest chain of mountains in South America are the Andes Mountains. The Andes are divided by the climate categories of Tropical, Dry and Wet Andes. This is the highest group of mountains outside of the continent of Asia.
a mountain range
It means "mountain chain" or "group of mountains." (ADDITIONAL INFO: It can also mean "Central mountain chain")