L = {M|M is a TM that accepts all even numbers}
For the above language i can have Tyes machine which has all even numbers.And Tno as machine whose language is empty.So i can say it is undecidable.
But to show it is Not RE. What should be my Tno,so that it should be proper superset of Tyes?Can i take sigma* as my Tno?Although it will accepts the even numbers ,but still it has odd numbers also.Will that work as Tno machine?I am assuming here that the property of the language as "Only all even numbers",i guess the same has been given in the question.