1) Basically a CPU’s clock keeps everything in the CPU synchronized.
CPUs are digital and like anything else digital, they work on the principle of “on” and “off” – however, transistors take time to fully switch on or off, and if you check for the state of one while it is transitioning, you will get unpredictable results. With a clock signal, we have something that says “by this deadline, this signal should be valid.” The other option is to have a second signal that says “I’m done, this signal is now valid” and I think that makes circuits much more complex.
2) Go here for the second answer Informative, Illustrative and easy to understand.
3) Go here for the third
4) The Fourth Very complicated, I say.
AND PLEASE Don’t ask so long questions, that is why I gave you links.
What is the need of a clock in a cpu ?
=> CPU is a sequencial machine, one tick, one cyle, one operation/ task/ job
What does synchronization mean in context of working of a cpu ?
=> too many things depending on the context, rougly it ensures that information has properly propageted before the next task started
How many instructions can be executed in one cycle ?
=> it depends on the architecture of the CPU
Can more than one instruction be executed in one cpu cycle ?
=> yes but, it depends on CPU architecture
as said above, there is plenty good books about that,