1.   What is kernel?

ans: Kernel is central part of an operating system that manages operations of computer and hardware. It basically manages operations of memory and CPU time.

2.   Is Linux an operating system or a kernel?

ans: Linux is a kernel. Its a part of a complete operating system. Many OS use Linus as there kernel. its a interface among application and hardware. 

3.   Is Linux Operating System Immune to Malware?

ans: No,Linux is more vulnerable than windows as its source code is open. But hacking into this system is not common as different version/types available.