Final answer:
The relation violates the 2nd Normal Form (2NF) due to partial dependency of a non-prime attribute on part of the candidate key.
Step-by-step explanation:
The relation r(a, b, c, d) with the functional dependencies (a, b) → c and a → d appears to violate the 2nd Normal Form (2NF). The violation occurs because there is a partial dependency of a non-prime attribute (c) on a part of the candidate key (a, b). To satisfy 2NF, all non-prime attributes must depend on the whole of a candidate key, not just part of it.