Candidate Key is $ab$.
Since all a,b,c,d are atomic so the relation is in 1 NF.
Checking the FDs :
$a\rightarrow c\ $ (Prime derives Non-Prime.)
$b\rightarrow d\ $ (Prime derives Non-Prime.)
Since, there are partial dependencies it is not in 2NF.
a} Answer 1NF but not 2NF