I don't understand exactly what you mean by 'different' by each of these cases based on your comments, but I'll try to guess that you mean something like 'comparability'.

a) It can be shown that there is a natural bijection between the real numbers R, and the cross product R x R. It follows that there is a bijection between R^n and R^m by induction since R^n for any n has the same cardinality.

b) I would say that a bijection that is as natural as the one in your comment works. Given a set of real values , not necessarily distinct, let A be an arbitrary element of C^n, for n fixed

If is the first entry, is your second entry, and so on, let B be a bijection which sends A to B with B a vector of elements, (you're just splitting the cells of A into 2 new cells of B)

An inductive argument can work to generalize.

c) I'll have to think more on c, because I'm not sure if it's the case that there exists a bijection between matrices and vectors.