What do you mean with P(2 by 1) ??

Is that a vector with 2 rows and 1 column?

If it is then there is no way P.X is defined with X being a 2 row 1 column vector.

2x1 2x1 is not defined.

P must be always a 2x2 matrix like in a and b.

Please explain better what do you mean for question c).