The correct answer is option 'B' - Instruction cycle.

The instruction cycle, also known as the fetch-decode-execute cycle or the instruction execution cycle, is the sequence of events that occurs in a computer when it is interpreting and executing an instruction. It consists of several steps that the computer goes through to fetch an instruction from memory, decode it, and then execute it.

Here is a detailed explanation of each step in the instruction cycle:

1. Fetch: In this step, the computer fetches the next instruction from memory. The program counter (PC) holds the address of the instruction to be fetched. The PC is incremented to point to the next instruction after the fetch. The instruction is then loaded into the instruction register (IR), which holds the current instruction being executed.

2. Decode: Once the instruction is fetched and stored in the IR, the computer decodes the instruction. The control unit of the CPU processes the instruction to determine what operation needs to be performed and what data is required.

3. Execute: After the instruction is decoded, the computer executes the instruction by performing the specified operation. This may involve performing arithmetic or logical operations, accessing memory, or transferring data between registers. The execution of the instruction modifies the state of the computer, such as updating the values in registers or memory.

4. Repeat: After the instruction is executed, the cycle repeats itself by fetching the next instruction. The PC is incremented again to point to the next instruction, and the process continues until the program is complete.

It is important to note that the instruction cycle is fundamental to the operation of a computer and is repeated for each instruction in a program. The cycle allows the computer to sequentially execute instructions, enabling it to perform complex tasks and carry out programs.