Explanation: Mercury is the nearest planet to the Sun. It is the smallest planet in the solar system and completes one revolution around the Sun in just about 88 Earth days. Due to its proximity, Mercury experiences extreme temperature variations between day and night.

Explanation: SONAR (Sound Navigation and Ranging) is a system used in ships and submarines to determine the depth of the ocean or to locate underwater objects. It works by sending sound waves into the water and measuring the time taken for the echo to return after reflecting from the seabed or any object.

Explanation: A monitor is an output device that displays text, images, and videos generated by the computer. It allows users to visually view the processed data. Common types of monitors include LCD, LED, and OLED screens.

ATM stands for Automated Teller Machine. It is an electronic banking device that allows customers to perform financial transactions such as cash withdrawals, deposits, fund transfers, and balance inquiries without the need for a human teller.

• All Time/Any Time Money: Common informal phrases, not the actual full form.
• Automatic Teller Machine: Incorrect; the correct term is Automated, not Automatic.

Explanation: Plants absorb nitrogen from the soil mainly in the form of nitrates (NO₃⁻). Inside the plant, nitrates are reduced to nitrites (NO₂⁻) and then to ammonia (NH₃) through the action of specific reductase enzymes. The ammonia thus formed is then used to synthesize amino acids, proteins, nucleic acids, and other nitrogen-containing compounds necessary for plant growth.

Simplified Pathway:

NO₃⁻ → NO₂⁻ → NH₃ → Amino acids → Proteins

Explanation: Sound waves travel fastest in solids, slower in liquids, and slowest in gases. This is because the speed of sound depends on the elasticity and density of the medium — it travels faster when particles are tightly packed and can transmit vibrations more efficiently. Among the options, iron (a solid) allows sound to travel much faster (around 5130 m/s) than in water (1500 m/s), ice (3200 m/s), or air (331 m/s at 0°C).

The Exosphere is the uppermost layer of the Earth's atmosphere. It lies above the thermosphere and gradually merges into outer space. The exosphere extends roughly from 700 km to 10,000 km above the Earth's surface. In this layer, air is extremely thin, and gas molecules such as hydrogen and helium are sparse and can even escape into space.

Other options (for context)

• Stratosphere: Second layer from the Earth’s surface; contains the ozone layer.
• Mesosphere: Lies above the stratosphere; meteors burn up here.
• Ionosphere: A region within the thermosphere important for radio communication, not the outermost layer.

Explanation: The speed of light is maximum in a vacuum (approximately 3 × 10⁸ m/s) and decreases as it passes through denser media. Among the given options — vacuum, air, water, and glass — light travels slowest in glass because glass has the highest refractive index (around 1.5). The greater the refractive index, the slower the light travels. This slowing down of light causes refraction, or bending of light, when it passes from one medium to another.

Explanation: The acid present in the human stomach is hydrochloric acid (HCl). It helps in the digestion of food by breaking down proteins and activating the enzyme pepsin. HCl also kills harmful microorganisms present in the food, aiding in maintaining a healthy digestive system.