Q. When the kernel has finished booting, what process is started?

Explanation by: Jatin Dubey

The Kernel is the part of the operating system that loads first, and it stays in the main memory. Generally, the Kernel is responsible for memory management, process management and disk management. The Kernel connects the system hardware to the application software. Every operating system has a kernel.
init is the parent of all processes on the system, it is executed by the kernel and is responsible for starting all other processes; it is the parent of all processes whose natural parents are dead and is responsible for picking them up when they die. The processes managed by init are called jobs and are defined by files in the /etc/init directory.