1.   What is kernel?
answer: kernel is central component of an operating system that manages operations of computer and hardware.

2.Is Linux an operating system or a kernel?
answer: The Linux kernel is the core component of the operating system. It provides essential services, such as process management, memory management, device drivers, and system calls, enabling the software and hardware to communicate with each other. It acts as an intermediary between the hardware and the software
running on the system.

3. Is Linux Operating System Immune to Malware?

An operating system can be assumed to be bug-free because it would be useless if it did.
I would answer "no" since computers are unable to differentiate between legitimate and dangerous software,
hence an anti-virus application is impossible.
A popular method for securing a system is to exclude programmers from using it and limit the software 
that can be run on it to that which has been authorized by management or the OS provider. 
Thus, the issue is reduced to blocking access to unauthorized programs. Here, a bug-free operating system without potential exploits helps, but people can still make mistakes or turn hostile.
A ROM in an embedded system might only contain one program, making it possible to change the software only
by physically changing the ROM. You wouldn't require an operating system in that scenario.
Perhaps a computer constructed using the Harvard architecture as opposed to the von Neumann design is more 
resistant to program modifications.