What is an acceptor impurity? Write the names of such impurities.

(N/A) An acceptor impurity is a trivalent element (an element with $3$ valence electrons) that is added to an intrinsic semiconductor (like Silicon or Germanium) to create a $p$-type semiconductor.
When a trivalent atom replaces a tetravalent atom in the crystal lattice,it creates a vacancy or a 'hole' because it has one less electron to form the required covalent bonds with neighboring atoms.
This hole acts as a charge carrier and can 'accept' an electron from the valence band,hence the name 'acceptor impurity'.
Examples of acceptor impurities include Boron $(B)$,Aluminum $(Al)$,Gallium $(Ga)$,and Indium $(In)$.