I am quite confused between

1. There aren't much of a differences

2. There aren't many differences

3. There isn't much of a difference

4. There isn't much difference

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

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