2. L is set of all CFL. For this language whether any member's complement is CFL or not is non trival property. As CFL are not closed under complement. So According to Rice theorem it is Undecidable.

3. L is set of all RL. For this language whether any member's complement is RL or not is trival property. As RL are closed under complement. So According to Rice theorem it is Decidable.

4. L is set of all Recursive languages. For this language whether any member's complement is Recursive languages or not is trival property. As Recursive languages are closed under complement. So According to Rice theorem it is Decidable.