Why Correct: The Central Pollution Control Board defines noise pollution as sound levels exceeding 75 dB during daytime (6 AM to 10 PM) and 70 dB during nighttime (10 PM to 6 AM) in residential areas.
Distractor Analysis: 50-60 dB represents normal conversation levels and is generally considered safe. 80-99 dB includes heavy traffic noise and can cause hearing damage with prolonged exposure, but pollution regulations use lower thresholds. 40-65 dB covers quiet indoor environments to moderate outdoor noise, below pollution limits.
Takeaway: The Noise Pollution (Regulation and Control) Rules, 2000 establish four zones with different limits: industrial (75 dB day/70 dB night), commercial (65/55), residential (55/45), and silence zones (50/40).

Why Correct: Sound travels fastest in solids because particles are closely packed, allowing faster transmission of mechanical vibrations through stronger intermolecular forces.
Distractor Analysis: Liquids transmit sound slower than solids but faster than gases due to moderate particle spacing. Gases have the slowest sound speed among normal media because particles are far apart with weak interactions. Vacuum cannot transmit sound at all since it lacks any medium for mechanical wave propagation.
Takeaway: The speed of sound in air at room temperature is approximately 343 m/s, while in water it's about 1482 m/s, and in steel it can exceed 5000 m/s.

Why Correct: Sound waves in air are longitudinal mechanical waves where particle oscillations occur parallel to the direction of wave propagation, creating compressions and rarefactions.
Distractor Analysis: Transverse waves have particle oscillations perpendicular to propagation direction, like light and water surface waves. Electromagnetic waves are transverse waves that can propagate through vacuum, unlike mechanical sound waves. Polarization refers to the orientation of oscillations in transverse waves, which doesn't apply to longitudinal sound waves.
Takeaway: Mechanical waves require a medium, while electromagnetic waves can travel through vacuum.

Why Correct: Music hall walls reflect sound to create reverberation, which enhances sound quality by allowing multiple reflections to reach listeners from different directions.
Distractor Analysis: Transmitting sound would let it escape, reducing volume. Absorbing sound would deaden the acoustic environment. Amplifying sound requires electronic equipment, not wall properties.
Takeaway: Reverberation time is the key acoustic parameter for halls, typically 1.5-2.5 seconds for music versus 0.5-1.0 seconds for speech halls.