The input & output impedance of an amplifier

WHAT IS THE input & output impedance of the AMPLIFIER...?
Rin>Rout
OR
RIn<Rout
is it varies form amplifier to amplifier....?

depend on the type of the amplifier.
for a generic op-amp ideally Rin = infinite and Rout = 0. In real life, the input impedance is indeed very high, however the output impedance is not zero.

For microwave amplifier, most are matched to 50 ohms for both input and output.

For Common emitter amplifier....if Rin is high(INFINITE) then how the base will be conduct?....Ib=0....then how the amplifier will work?

Rin never will be infinite. Always Ib>0 !
Besides this, you have to discriminate between static and dynamic input impedance.