Question

What is meant by pair annihilation? Write a balanced equation for the same.

Answer 1

When an electron $e^{-}$ and a positron $e^{+}$ (i.e. electron's antiparticle) at low energies collide, they annihilate to produce two gamma photons each of energy $0.511MeV$.
Balanced equation : $e^{-}+e^{+}\to \gamma +\gamma$
The above process is governed by conservation of electric charge, conservation of linear momentum, angular momentum and total energy.