Explanation:

An ALU (Arithmetic Logic Unit) is a component of a computer processor that performs arithmetic and logical operations. It is responsible for carrying out calculations and logical comparisons required for the execution of instructions.

On the other hand, a control unit is responsible for managing and coordinating the activities of all the components of a computer system. It is responsible for fetching instructions from memory, decoding them, and executing them by controlling the flow of data between different components.

A microprocessor is a central processing unit (CPU) that integrates both the ALU and the control unit on a single chip. It is the "brain" of a computer system, responsible for executing instructions and performing calculations.

Now, let's analyze the given options and determine which one is correct:

a) ALU and control unit on a single chip
This option is partially correct because a microprocessor does indeed integrate both the ALU and the control unit. However, it is not solely these two components on the chip.

b) ALU and memory on a single chip
This option is incorrect. While some microprocessors may have cache memory integrated on the chip, the primary memory (RAM) is typically separate from the microprocessor.

c) Register unit and I/O device on a single chip
This option is incorrect. The register unit is a component of the microprocessor and is responsible for storing temporary data during the execution of instructions. I/O (Input/Output) devices, on the other hand, are external devices connected to the microprocessor.

d) Register unit and control unit on a single chip
This option is correct. The register unit and the control unit are both components of the microprocessor, and a microprocessor integrates both of them on a single chip. The register unit stores temporary data, while the control unit manages the execution of instructions.

Therefore, the correct answer is option 'D' - Register unit and control unit on a single chip.