On the Solvability of 8-Puzzle

$$P_1 = \begin{bmatrix}a &\Box & b \\ c&d&e \\ f&g&h \\ \end{bmatrix} \rightarrow P_2 = \begin{bmatrix}a&d&b \\ c&\Box&e \\ f&g&h \\ \end{bmatrix}$$