In the 8085 microprocessor, a subroutine is a reusable block of code that is invoked with a CALL instruction. When CALL executes, the processor automatically saves the address of the next instruction (the return address) by pushing the 16-bit Program Counter onto the stack and decrementing the Stack Pointer (SP) by 2. To come back to the main program, the reverse operation is needed, and that is exactly what RET does.

The RET instruction performs the following:

1. It pops the two bytes of the return address from the top of the stack back into the Program Counter (PC).
2. The Stack Pointer is incremented by 2, restoring it to the value it had before the CALL.
3. Execution then continues from the instruction immediately following the original CALL, so the program resumes seamlessly.

RET is the unconditional return. The 8085 also provides conditional returns (RC, RNC, RZ, RNZ, RP, RM, RPE, RPO) that return only when a specified flag condition is satisfied.

The other choices do not return from a subroutine. CALL does the opposite of RET — it transfers control into a subroutine and saves the return address. RST (Restart) is a special one-byte call to a fixed vector location, typically used for interrupts, not for returning. JMP merely changes the Program Counter to a new address without using the stack, so it neither saves nor restores any return address and cannot bring control back to the caller.