How many pairs of perpendicular lines are there in the given figure?

Perpendicular lines are lines that cut each other at a right angle. For example, the figure following is one pair of perpendicular lines.

In the figure given in the question, 

1. line p is perpendicular to line j 
2. line p is perpendicular to line n,  
3. line q is also perpendicular to line j and 
4. line q is perpendicular to line n. 

Hence there are total 4 pairs of perpendicular lines.