An artificial satellite can be tracked very precisely from the earth by using

The answer is A) Doppler effect. A satellite's position and velocity are tracked by measuring the shift in frequency of the radio signal it transmits. As the satellite approaches, the received frequency rises; as it recedes, it falls. Measuring this shift continuously gives precise range-rate data, and from it the orbit can be determined very accurately. The US Transit navigation system worked on this principle, and ground stations still use Doppler measurements for orbit determination.

Why the others fail:

• B) Radar: radar can detect and range satellites and is used for surveillance and debris tracking. It is a real tool, but the precise tracking the question points to is the Doppler measurement. This is the main point of debate in the question.
• C) Sonar: works with sound waves in water. Sound cannot travel through the vacuum of space, so it cannot reach a satellite.
• D) Pulsar: a rapidly rotating neutron star emitting regular pulses. It is a celestial object, not a tracking method.

Core concept: Doppler shift applied to radio tracking. Mains link: space situational awareness, satellite navigation and ISRO's tracking network.

Trap: choosing radar because it is the first tool that comes to mind for tracking. Radar is used, but the classic answer for precise satellite tracking is Doppler.