Answer:
Exponent or index
Step-by-step explanation:
An exponent or index is a number or letter written above and to the right of a mathematical expression called the base.
It indicates that the base is to be raised to a certain power.
Here,
3, 4 and 12 are the letters which are written above the base 2.
So,
3, 4 and 12 are exponent or index
