Explanation:

The question asks for the definition of virtual memory, a crucial concept in operating systems and memory management. Option (a) Memory of hard disk which is used by CPU as extended RAM: This statement accurately describes virtual memory. Virtual memory is a memory management capability of an operating system that uses hardware and software to allow a computer to compensate for physical memory (RAM) shortages. It achieves this by temporarily transferring data from RAM to disk storage (typically a dedicated file or partition on the hard disk, often called a swap file or paging file). This makes it appear to programs as if there is more RAM available than physically installed. The CPU, with the help of the Memory Management Unit (MMU), maps virtual addresses used by programs to physical addresses in RAM or to locations on the hard disk. Thus, a portion of the hard disk effectively acts as an extension of the computer's RAM, allowing more programs or larger programs to run than would fit in physical RAM alone. This is the precise definition and function of virtual memory. Option (b) Located in RAM: This statement is incorrect. Virtual memory is a *concept* that *extends* the apparent size of RAM, but the 'virtual' part of the memory is primarily located on the hard disk (in the swap file). Physical RAM is distinct from the hard disk space used for virtual memory. While the operating system manages the movement of data between RAM and the swap file, virtual memory itself is not *located* in RAM; rather, it *utilizes* hard disk space to supplement RAM. Therefore, this option is factually wrong. Option (c) It needs when there is no any RAM in computer: This statement is fundamentally incorrect. A computer cannot function without physical RAM (Random Access Memory). RAM is essential for the CPU to execute instructions and store data that is actively being used. Virtual memory is a supplementary mechanism that helps when there is *insufficient* RAM, not *no* RAM. It allows the system to handle more processes or larger processes than physical RAM can hold, but it always requires physical RAM to operate. Without any RAM, the computer simply wouldn't boot or run any software. Therefore, this option describes an impossible scenario and misunderstands the role of virtual memory. Option (d) Backup device for floppy discs: This statement is completely unrelated to virtual memory. A 'backup device for floppy discs' would refer to a storage medium (like another floppy disk, a CD, or a hard drive) or a utility used to create copies of data from floppy disks for data recovery purposes. Virtual memory is a system-level memory management technique, not a data backup solution or a device for old storage media. Therefore, this option is irrelevant and incorrect. Option (e) None of these: This option would be correct only if none of the other options accurately defined virtual memory. However, option (a) provides a precise and correct definition of virtual memory. Therefore, a correct answer is present, making 'none of these' incorrect.