What are the number of bonding pairs and lone pairs of electrons in #H_2O#?
Bonding pair is a pair of electrons that is shared by two atoms to form a covalent bond. Lone pairs on the other hand are pairs of electrons that do not take part in bonding.
To identify which is which, you have to write down the Lewis structure. The Lewis structure of water is found below.
Since, there are two Hydrogen attached to a single Oxygen we can say that
Two atoms bonded to the central atom, Oxygen = Two bonding pairs
Four electrons that do not participate in bonding = Two lone pairs