new [], delete [] complexity

Question

I already know that the new[] operator first allocates memory and then calls the constructor for each element and that the delete[] operator first call

Answer 1

But if I have a class, for which I have not defined any constructor/destructor, will the complexity still be O(n), or will it be just O(1)?

The members themselves might still have destructors. In short, for PODs, delete[] will be O(1).