Correct Option (d):
Thunder is the sound phenomenon that accompanies lightning during a thunderstorm. It is not directly produced by the clouds themselves or by air and water particle movements. The actual mechanism involves the rapid heating of air by a lightning discharge. When a lightning bolt travels through the atmosphere, it heats the air in its path to extremely high temperatures (e.g., around 30,000°C) in a fraction of a second. This sudden and intense heating causes the air to expand explosively, generating a powerful shockwave. This shockwave then propagates as sound waves, which are perceived as thunder.
Incorrect Options:
- Statement 1: "Meeting of cumulonimbus clouds in the sky." Cumulonimbus clouds are the storm clouds associated with lightning and thunder. However, the physical meeting or collision of these clouds does not directly produce the sound of thunder. Thunder is a consequence of the electrical discharge (lightning) within or between these clouds.
- Statement 2: "Lightning that separates the nimbus clouds." While lightning is the direct cause of thunder, the description "separates the nimbus clouds" is factually incorrect. Lightning is an electrical discharge and does not physically separate clouds. The sound of thunder originates from the rapid thermal expansion of air along the lightning channel.
- Statement 3: "Violent upward movement of air and water particles." Violent upward movement of air and water particles (convection) is a crucial process in the formation and development of cumulonimbus clouds and thunderstorms, leading to charge separation necessary for lightning. However, this atmospheric movement itself does not directly produce the sound of thunder. Thunder is a direct acoustic outcome of the lightning discharge.