Is else is required in else if statement.
No it is not compulsory to use 'else' after 'if'. But it is compulsory to use 'if' before 'else'. In one sentence 'if' is compulsory but 'else' is optional
You need not have an "else" after "if", it is just used to do something if at all your "if" fails.
No it's not essentially to have "else" block, bz it's executes only if the given condition is false in "if" block.