I think it is TRUE
Because, intransitivity means A -> B , B -> C but A should not gives C
From the given Question if A is a key, and C is a prime attribute and B is non key
3NF follows 2 conditions
Key --> anything
anything --> Prime attribute
A -> B (3NF because A is key)
B -> C (3NF because C is prime attribute)
and there must be no relation of A--> C. hence A and C are intransitive.
But still it follows 3NF properties, Hence the statement is true.