1. What is kernel? 

Kernel is a computer program that's work when an OS start. Kernel do the job between hardware and software. When a software work, it's need some recommend devices like keyboard , mouse, sound system etc. we do not need to connect them manually , kernel do this job by himself. Kernel do our job very easier. 

2. Is Linux an operating system or a kernel? 

Linux not an operating system. Linux is kernel. Generally people call Linux as an operating system , but is not true. Linux is come from glue Linux operating system it's work like a kernel. 

3. Is Linux Operating System Immune to Malware? 

The answer is Yes. Linux immune like the other Operating System. As we know Linux is an open source Operating System it's also immune to malware.