RE: someone please explain difference between 2 and 4 strokes..
Sachin,
As Bill wrote, the RPM ranges are a generality.
The two-stroke has a power stroke on every revolution, while a four-stroke has one on every other revolution. So, even though the four-stroke has more effective scavenging and a higher combustion pressure, the two-stroke will produce more absolute torque.
If a two-stroke and a four-stroke are timed to produce their torque at the same RPM, the two-stroke will be capable of spinning a significantly larger prop.