Question

Few organic questions I have doubts on:

Answer 1

1.Number of optically active isomers observed in 2,3-dichlorobbutane is _____.

Due to plane of symmetry I think its 0. But the answer given is 2.Why?

2.What is the reason for highest acidity in o-nitro benzoic acid?

I read in my text that it speaks on steric hindrance. But what is the relation between steric hindrance and acidity? Can anyone explain this?

3.Arrange in increasing order of acidity:



I am confused on this one.

4. Which of the foll is strongest acid and why?



5. Number of possible isomers for C4H8 are _____

I am getting 4 but the answer given is 3