How does the 8085 microprocessor instruction register work?

There is no exit instruction in the 8085. Do you mean return, as in from a function or interrupt? If so, the instruction is RET.

First of all 8085 is nt Micro processor its Micro controller....There are four types of instructions...Data transferarithmeticlogicalbranch

6 general purpose registers.i.e., B,C,D,E,H,L

The NOP instruction is a no-operation instruction. It does nothing to the state of the machine, except to use some time. In the case of the 8085, it uses four clock cycles plus however many wait...

the purpose of mvi is to 8 bit data immidiatly to the register or memory example mvi b,05h will move 05h to register b