Question

all chiral centre is srereogenic centre but all stereogenic centre are not chiral centre why....?

Answer 1

A carbon atom carrying 4 different groups is a stereogenic or chiral centre
whereas a sterocentre is a point in a molecules where the exchange of 2 groups will produce a stereoisomer.

Answer 2

A carbon atom carrying four different groups is a stereogenic or chiral centre. For those who recognize a difference, the difference is that "stereocentre" or “stereogenic centre” is the more general term. A stereocentre is a point in a molecule where the exchange of two groups will produce a stereoisomer.