The correct option is
i.e.,
.
Further explanation:
Concept used:
The associative property of the addition states that the addition of numbers cannot affect by the grouping of the number.

Here, in the above equation the value of
is always equal to the value of
whether the grouping of number is changes or not.
Calculation:
Now check the option to get the answer.
First check option (a)

In the above equation the grouping of the number is changed.
Now check the values of left hand side and right hand side.

The value of LHS is same as RHS.
Therefore, option (a) is correct.
Now check option (b)

The term
should be associated with
but it is associated with
.
Therefore the option (b) is incorrect.
Now check option (c)

The above expression does not follow any property.
Therefore the option (c) is incorrect.
Now check option (d)

The above expression follows additive property not associative property.
Therefore the option (d) is incorrect.
Thus, the correct option is
i.e.,
.
Learn more:
1. A problem on simplification: brainly.com/question/573729
2. A problem on domain and range: brainly.com/question/3412497
Answer details:
Grade: Junior school
Subject: Mathematics
Chapter: Simplification
Keywords: Associative property, equation, property, addition, associative property of Addition, additive property, grouping terms, left hand side, right hand side, LHS, RHS.