The key for relation will be composite {A,B}
A+ = {A,C}
B+ = {B,D}
{A,B}+ = {A,B,C,D} so it is the key
prime attributes = {A,B} (members of key}
non prime attributes = {C,D}
since all attributes contain atomic values it is in first normal form
non prime attribute C is partially dependent on key (A --> C}
non prime attribute D is partially dependent on key (B --> D}
for a relation to be in second normal form
all non prime attributes should be fully dependent on key
but here non prime attributes are partially dependent. Clearly it is not in second normal form
First normal form but not in second normal form.