Why 8 cylinders are present in an engine?

Answer 1

First of all not engines have 8 cylinders, there can be both fewer and more of them.

But 8, particularly in a V-formation has turned out to be a fairly useful configuration. If you want the same power from a smaller number, the cylinders have to be bigger, which means that you have to build them stronger. If you wanted the same power from more cylinders, you could build each cylinder smaller, but you'd need more parts that have to fit together just right.

On top of that, with 8 cylinders, you get a nice distribution of the power contribution from each cylinder, making the engine run smoothly. With fewer cylinders, each power push will be further apart, making it a bit jerky...