To answer this question, you need to understand the basic components of a computer and their functions.
When you power on a computer, it starts executing instructions from the ROM (Read-Only Memory). ROM is a type of memory that contains firmware or permanent instructions that the computer needs to start up and perform basic functions. It is non-volatile, meaning that the data stored in ROM is not lost when the power is turned off.
RAM (Random Access Memory) is a volatile memory that is used by the computer to temporarily store data and instructions that are actively being used. It is not used to execute instructions when the computer is powered on.
Hard Disk is a storage device that stores data and programs in a non-volatile manner. It is not involved in executing instructions when the computer is powered on.
Therefore, the correct answer is A) ROM. When you power on the computer, it starts executing instructions from the ROM.