Electrically charged particles from space travelling at speeds of several hundred km/sec can severely harm living beings if they reach the surface of the Earth. What prevents them from reaching the surface of the Earth?

Electrically charged particles from space travelling at speeds of…

The Earth's magnetic field diverts them towards its poles.
Ozone layer around the Earth reflects them back to outer space.
Moisture in the upper layers prevents them from reaching the surface of the Earth.
None of the statements (a), (b) and (c) given above is correct.

Answer

(a) Charged particles from the Sun/cosmic space are largely deflected by the Earth’s magnetosphere; many are guided toward the polar regions, causing auroras. Verdict: Correct.
(b) The ozone layer mainly absorbs harmful ultraviolet radiation; it does not reflect charged particles back to space. Verdict: Incorrect.
(c) Moisture/water vapour in upper layers is not the main shield against high-speed charged particles. Verdict: Incorrect.
Since only (a) is correct, the answer is (a).