When we say a class of languages is decidable we mean that the membership problem can be solved. However even though the membership problem is solvable for the class, there may exists some problems for the same class which are undecidable. For example Context free languages are decidable yet the problem of determining whether the language generated by context free grammar is unambiguous is undecidable.
I want to know some undecidable problems for recursive languages. Please don't problems related to context free and context sensitive language and then say that these languages are also recursive. The problems I want must be for only recursive languages and not for any proper subset of this class.