How many wire pairs in a cat 5 cable are actually used for transmission and reception on a 10 base t network?

Twisted pair cabling has 4 pairs of wires (8 wires in total), but 10BASE-T and 100BASE-TX requires only 2 of those pairs (4 wires in total).

Exams will often try to trick you by asking questions like 10baseT uses how many pairs so you think you're being asked how many pairs does it have? When really you're just being asked how many pairs does it use.