The period of one revolution of a geostationary satellite is

Answer: (a) 24 hours

A geostationary satellite orbits once in ~24 hours (one sidereal day) at ~36,000 km, so it stays over one spot.

The idea

A geostationary satellite must move around Earth at the same angular rate as Earth turns. Its orbit must also be circular, above the equator and in the same direction as Earth’s rotation. Together these conditions keep it above one ground location.

Place satellite in a circular equatorial orbit → Make it travel west to east → Match its orbital period to Earth’s sidereal rotation → Satellite and ground turn at the same angular rate → Satellite stays over one longitude

Elimination technique

Remaining fixed above a ground point requires matching Earth’s daily rotation, so month-long, year-long and two-day periods can be rejected.

Also know

The exact matching period is one sidereal day, about 23 hours 56 minutes; 24 hours is the rounded exam answer. A geosynchronous orbit matches that period but need not keep a satellite over one point. Polar satellites pass over changing regions and are useful for mapping and Earth observation.