Parity error detection, 4-bit example of how a particular scheme doesn't work

Question

Hey so I'm doing a bit of revising for a midterm next week, and I have this question that I'm not being able to find the material or understand how to answer.

I can see how a single error, double or triple error happens, but I am not sure how a 4-bit error would look like.

Answer 1

If you have any 2x2 block

1  0
0  1

and invert every bit in this block, then the parity is not changed on any row or column.