During the Instruction Cycle, which specific register holds the instruction that is currently being decoded and executed by the CPU?

Correct — C. In the instruction cycle the CPU fetches an instruction from the memory location the program counter points to, then loads it into the Instruction Register (IR).

The IR holds that instruction while the control unit decodes and executes it.

The register holding the current instruction is the IR → option (c).

Why the others are wrong

• (a)
  Memory Address Register (MAR) — The MAR holds a memory address, the location to be read from or written to, not an instruction. During a fetch it says where to look, and the instruction found there is loaded into the IR.
• (b)
  Program Counter (PC) — The Program Counter holds the address of the next instruction and is usually incremented after each fetch. It points ahead, while the IR holds the instruction being decoded now.
• (d)
  Accumulator (AC) — The Accumulator stores intermediate results from the arithmetic logic unit: the data being worked on, not the instruction doing the work.

The instruction cycle is the loop a CPU repeats for every instruction: fetch, decode, execute. The four registers in the options have separate jobs in it.

PC: the address of the next instruction.
MAR: the address memory is about to read or write.
IR: the instruction just fetched, held while it is decoded and executed.
Accumulator: intermediate results from the ALU.

Key facts

• Program Counter (PC): address of the next instruction, usually incremented after each fetch.
• Instruction Register (IR): the instruction currently being decoded or executed.
• Memory Address Register (MAR): address of the memory location being read or written.
• Accumulator: intermediate results of arithmetic and logic operations.

Common traps

• Choosing the Program Counter because it deals with instructions, when it holds the next instruction's address, not the current instruction.
• Choosing the MAR because the instruction comes from memory, when the MAR holds an address, not an instruction.

No directly related past PYQ was found.