"isn't much" vs "aren't much" vs "aren't much of"

Question

I am quite confused between

1. There aren't much of a differences between those two

2. There aren't many differences between those two

3. There isn't much of a difference between those two

4. There isn't much difference between those two

Can anyone point out the right ones and explain why please? Thank you

Answer 1

Gramatically correct sentences are 2, 3 and 4.

• "much of a" refers to a singular subject
• "much" refers to a quality
• "many" refers to a plural subject

In number 1, the subject is "differences" which is plural.