Correct Answer - Option 4 : auto decrement
Index addressing mode:
In this, effective address of operand is obtained by adding the content of index register and address part of instruction.
Indirect addressing mode:
In this, address field specifies the memory location that contains effective address of operand.
Auto increment addressing mode:
In this addressing mode, effective address is the content of register and after accessing operand, content of register is incremented.
Auto decrement addressing mode:
In this addressing mode, the contents of a register specified in the instruction are first decremented and these contents are used as effective address of operand.
Therefore option 4 is correct.