Question

Anyone can tell me about1 2 3 coordination no.

Answer 1

basically co-ordination number is the no. of atoms surrounding a central atom in a lattice of a solid. unit cell is the smallest part of the lattice.
If a unit cell has co-ordination number 1 , that means the central atom has one atom surrounding it.
if a unit cell has co-ordination number 2 , that means the central atom has 2 atoms surrounding it.

co-ordination number is different for different types of lattices.
Thank you,
hope u understood!