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Membership problem of Recursive languages are decidable.

My approach:

Let L be a recursive language and M be the Turing Machine that accepts it. For string w, if w ∈ L, then M halts in final state. If w ∉ L, then M halts in non-final state. (halts always!). That’s why Recursive languages are decidable.

My question is in same logic, why finiteness, emptiness is undecidable? Don’t want any concrete proof. I just want brief concepts like my approach.