1. What is Kernel?

The kernel is the essential foundation of a computer's operating system (OS). It is the core that provides basic services for all other parts of the OS. The kernel is a central component of an operating system. It manages the operations of computers and hardware and basically manages operations of memory and CPU time. It is that part of an OS that loads first and remains in the main memory. Examples are Zircon, Linux, WindowsNT, etc. 

2.  Is Linux an operating system or a kernel?

Actually, Linux is just a kernel, not an operating system. Linux has so many distros or distributors like Kali, ubuntu and so many others.  This Linux term is used to refer to a complete OS (operating system). There includes a shell and command line and GUI tools to control the system.

3. Is Linux Operating System Immune to Malware?

A misconception in our mind that Linux systems are immune to viruses. Viruses, as well as other forms of malware. It can infect Linux systems. When Linux system is effected in virus it does not get access the root file. So that viruses or malware harmed local file.