The correct answer is "
The store was a massive, exciting place to shop"
Explanation:
In grammar, the comma is a punctuation mark used mainly to introduce a short pause between certain elements in a sentence, because of this, it is common to use the comma to separate elements that belong to the same category in a list; use comma to separate adjectives, use comma to separate dependent and independent clauses and use comma to separate introductory clauses or clauses that provide extra information . On the other hand, the comma should never be used to separate the subject from the verb, the verb from the object or complement or articles such as a, or, the from the noun these are linked to. Considering this, in the case of the sentence "The store was a massive exciting place to shop" the correct way to use the comma is "The store was a massive, exciting place to shop" because in this case the comma is used to separate two adjectives or elements that belong to the same category in the sentence which is correct according to grammar.
