B is a proper subset of C If the cardinal number of C is 8 what is the maximum number of elements in B?

If every element of B is contained in C, then B is a subset of C. If every element of B is contained in C and B is not the same as C, then B is a proper subset of C.

The cardinal number of a set is the number of elements in the set.

In this case, C has 8 elements, so B has at most 7 elements.