Number of ways of selecting two squares having common side in a chess board is (1 unit size squares)

$$\begin{gathered} \text{ In each row, there are }7\text{ possible pairs of adjacent squares. } \\ \text{ So there are }7\times 8=56\text{ pairs of horizontally adjacent pair of squares. } \\ \text{ Similarly, in each column, there are }7\text{ possible pairs of adjacent squares. } \\ \text{ There are }7\times 8=56\text{ pairs of vertically adjacent}\text{s pair of quares. } \end{gathered}$$

$\text{ total number of }\mathrm{pairs} \mathrm{of} \mathrm{adjacent} \mathrm{squares}. 56+56=112$