Which component is responsible for executing instructions in a computer?

The Central Processing Unit (CPU) is the component responsible for executing instructions in a computer. It serves as the brain of the computer, performing calculations and processing data by following the instructions provided by the software. The CPU carries out the fundamental operations of fetching, decoding, and executing instructions from programs, enabling the system to perform tasks.

The CPU's architecture is designed to handle various operations, including arithmetic and logical operations, as well as control operations that manage the sequence and execution of instructions. Its high-speed capabilities allow it to process millions to billions of instructions per second, making it a critical component for overall computer performance.

In contrast, the other options serve different purposes and do not perform instruction execution. Expansion cards enhance the computer's capabilities but do not execute instructions. Storage devices, such as hard drives or SSDs, are responsible for storing data and programs but do not process or execute those programs. The power supply provides the necessary electrical power to the computer components but does not play a role in data processing.