Answer:
Coordination number:
Coordination number can be defined as the number of nearest atoms which touch the central atom.In simple word the number of neighbours atoms which touches a an atoms.
Atomic packing factor :
It is also known as packing efficiency.It is the fraction of volume in a Crystal which is filled by constituent particles.It is always less than 1.Generally it is represented in the fraction.
Ex:
Lets take FCC cubic cell
Coordination number = 12 .
Atomic packing factor = 74%
