What is the difference between chiral and achiral carbon

Chiral: The objects which are non-superimposable on their mirror image are called chiral. For e.g. a pair of hands. Your left and right hands look similar but if you put your left hand on your right hand, they do not coincide.

• If 4 valencies of carbon are satisfied by 4 different substituents, then Carbon is asymmetric and is called chiral, e.g. Butan-2-ol. The mirror images are called enantiomers.

Achiral: The objects which are superimposable on their mirror image are called achiral. For e.g. all identical objects like spheres. 

• The symmetric carbon in which 2 or more valencies are satisfied by the same substituents is achiral, e.g. Propan-2-ol