Explanation:

Multiplexer:
A multiplexer, also known as a mux, is a combinational circuit that selects one of many inputs and forwards the selected input to a single output line. It is commonly used in digital systems to select between multiple data sources or control signals.

Control Unit:
The control unit is responsible for controlling and coordinating the operations of the computer system. It generates control signals that determine the sequence of operations to be performed by the computer's various components, such as the ALU (Arithmetic Logic Unit), memory, and input/output devices.

ALU Operations:
The ALU (Arithmetic Logic Unit) is a digital circuit that performs arithmetic and logical operations on binary data. It can perform operations such as addition, subtraction, multiplication, division, bitwise AND, bitwise OR, etc.

Conditional Codes:
Conditional codes are flags or bits that are set or cleared based on the outcome of a previous operation. They are used to indicate the result of a comparison or a specific condition. Examples of conditional codes include zero flag, carry flag, overflow flag, etc.

Explanation of the answer:
The correct answer to the given question is option 'B' - Multiplexer.

A multiplexer is used to choose between incrementing the PC (Program Counter) or performing ALU operations. In a computer system, the PC is responsible for storing the address of the next instruction to be fetched and executed.

During the execution of a program, the PC needs to be incremented after each instruction is executed to point to the next instruction. However, there are certain instructions that require the PC to remain the same or modify it based on certain conditions. In such cases, a multiplexer is used to select between the incremented PC or a modified PC value based on the condition specified by the instruction.

The multiplexer takes the incremented PC and the modified PC value as inputs, along with a control signal from the control unit. Based on the control signal, the multiplexer selects one of the inputs and forwards it to the output, which becomes the new value of the PC.

This selection process allows the computer system to choose between incrementing the PC or performing ALU operations based on the specific requirements of the instruction being executed.