We are asked to find out which of the given expression is in the simplest form.
Let us analyze each of the given expression
Option 1:
It seems that this expression is already in its simplest form.
Option 2:
As you can see, the constant terms can be added together.
So this expression was not in its simplest form.
Option 3:
This expression may be further simplified as
So this expression was not in its simplest form.
Option 4:
This expression may be further simplified as
So this expression was not in its simplest form.
Therefore, now we know for sure that expression 1 was in its simplest form.