The part of primary memory that consists of important information necessary to execute user and application programs is:
ROM (Read-Only Memory)
- ROM is a type of primary memory that contains pre-programmed data that cannot be modified or erased by normal computer operations.
- It is non-volatile memory, meaning the data stored in ROM is retained even when the computer is turned off.
- ROM holds important information such as the computer's firmware, the BIOS (Basic Input/Output System), and other essential instructions required for booting up the computer and initializing hardware components.
- The data stored in ROM is permanently written at the time of manufacturing and cannot be altered by the user or applications.
- It provides the necessary instructions for the computer to start up and load the operating system, allowing user and application programs to execute.
In contrast:
RAM (Random Access Memory)
- RAM is another type of primary memory that is volatile, meaning it loses its data when the computer is powered off.
- RAM is used to temporarily store data and instructions that are actively being used by the computer's processor.
- It is faster to access than secondary storage devices such as hard disks, making it ideal for quickly retrieving and executing instructions.
- However, RAM does not hold important system information like ROM does. Its contents are constantly changing as programs are loaded and executed.
Hard Disk
- While hard disks are a form of primary storage, they are not part of "primary memory" as referred to in the question.
- Hard disks are secondary storage devices used for long-term data storage and are not directly involved in executing user and application programs.
Therefore, the correct answer is ROM as it contains the important information necessary for executing user and application programs.

As hard disc is secondary memory, it's wrong.
RAM is dependent on power supply, it's wrong.
The option left is ROM.
So, B is correct.