How many pairs of sides touch each other in a rectangle of 4 squares in each 2 rows

10 pairs of side touch.

So,

You made a 2 x 4 rectangle, composed of squares.

Visualizing this setup, we can first see that the 4 squares lengthwise touch each other in pairs. So that's 4 already.

In addition, notice that there are three columns in the widths. Also notice that each column has 2 pairs of touching sides. So 2 * 3 = 6 more pairs.

6 + 4 = 10

There are 10 pairs of sides that touch each other.