Sericulture is the rearing and cultivation of silkworms for the production of silk. The process involves raising silkworms on mulberry leaves, harvesting their cocoons, and then extracting silk fibers from these cocoons. The most commonly used silkworm species is Bombyx mori. Sericulture is an important cottage industry in countries like India, China, and Japan.

Other options (for context)

• Fishes: Their rearing is called Pisciculture.
• Honey bees: Their rearing is called Apiculture.
• Earth worms: Their cultivation for composting is called Vermiculture.

Explanation: The permissible noise level in residential areas should not exceed 55 decibels (dB) during the daytime and 45 dB at night, as per the Central Pollution Control Board (CPCB) guidelines. Exposure to higher noise levels can lead to stress, disturbed sleep, and hearing impairment.

Explanation: Nitrogen (N₂) constitutes the major portion of the Earth's atmosphere by volume — about 78%. It is a colorless, odorless, and inert gas that plays a vital role in maintaining atmospheric stability and supporting life through the nitrogen cycle. Oxygen makes up about 21% of the atmosphere and is essential for respiration and combustion. Other gases like argon (~0.93%) and carbon dioxide (~0.04%) are present in much smaller amounts.

Helium is used instead of nitrogen in the breathing mixture for deep-sea divers. At high pressures underwater, nitrogen can dissolve in blood and cause nitrogen narcosis or “rapture of the deep.” Helium, being inert and less soluble in blood, prevents this condition and makes breathing easier under pressure.

• Argon, Xenon, Krypton: Inert gases but not suitable due to higher density and narcotic effects.

Explanation: The pyloric sphincter is a circular band of smooth muscle located at the junction of the stomach and the duodenum (first part of the small intestine). It regulates the passage of partially digested food (chyme) from the stomach into the small intestine and prevents backflow. The cardiac sphincter, by contrast, controls food entry into the stomach from the esophagus.

Explanation: Bullets are typically made of lead or lead alloys because lead is dense and malleable. When bullets remain lodged in the body, they can corrode over time and release lead ions into surrounding tissues and blood, resulting in chronic lead poisoning (plumbism). Symptoms include abdominal pain, anemia, fatigue, headache, irritability, and neurological disorders. In severe cases, it may cause kidney and brain damage.

Prevention: Complete removal of bullet fragments and regular monitoring of blood lead levels in affected individuals are essential to prevent toxicity.

A Lunar Eclipse occurs when the Earth comes between the Sun and the Moon, causing the Earth’s shadow to fall on the Moon. This alignment blocks the sunlight that normally reflects off the Moon’s surface, making it appear dark or reddish (known as a Blood Moon). Lunar eclipses only occur during a full moon when the Sun, Earth, and Moon are in a straight line (or nearly so).

Other options (for context)

• When Sun is between Earth and Moon: Incorrect — this alignment causes no eclipse.
• When Moon is between Earth and Sun: This alignment causes a solar eclipse, not a lunar one.
• When Earth is between Sun and other celestial bodies: Too general — lunar eclipse specifically involves the Moon.

Explanation: EDUSAT (Education Satellite) was launched by the Indian Space Research Organisation (ISRO) in September 2004. It was the first Indian satellite built exclusively for educational purposes, designed to provide distance learning and interactive education through satellite communication.