The magnetic effect of current gives rise to a mechanical force. When an electric current passes through a conductor placed in a magnetic field, it experiences a force that can cause motion — this is known as the motor effect. This principle is used in devices like electric motors, galvanometers, and loudspeakers.

• Frictional force: Arises due to contact between surfaces.
• Spring force: Related to elasticity.
• Gravitational force: Due to attraction between masses, unrelated to current.

Coal is a fossil fuel formed from the remains of plants that lived and died millions of years ago. Over long geological periods, heat and pressure converted these plant remains buried under soil and rock into coal. It is a major source of energy used for electricity generation, steel production, and various industrial processes. However, burning coal releases carbon dioxide, contributing to air pollution and global warming.

Other options (for context)

• Solar energy: A renewable energy source derived from sunlight, not a fossil fuel.
• Quartz: A mineral composed of silicon and oxygen, not an energy source.
• Lava: Molten rock from volcanic eruptions, not a fossil fuel.

Explanation: The Bhopal Gas Tragedy occurred on the night of December 2–3, 1984, at the Union Carbide pesticide plant in Bhopal, Madhya Pradesh (India). The disaster was caused by the accidental leakage of Methyl Isocyanate (MIC), a highly toxic and reactive gas used in pesticide manufacturing. The poisonous gas spread rapidly over the nearby populated areas, killing thousands of people and causing severe respiratory and neurological disorders. It is considered one of the world’s worst industrial disasters.

The full form of LAN is Local Area Network. It is a network that connects computers and devices within a limited geographical area such as a home, office, school, or building. LANs enable data sharing, resource sharing (like printers or internet connections), and communication between connected devices. Common technologies used in LANs include Ethernet and Wi-Fi.

Other options (for context)

• Line Area Network: Incorrect — not a recognized networking term.
• Linear Area Network: Incorrect — there is no such standard network type.
• Land Area Network: Incorrect — misinterpretation of LAN abbreviation.

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: Brass, an alloy of copper and zinc, gets discoloured when exposed to air containing hydrogen sulphide (H₂S). The H₂S reacts with the metal surface to form a dark layer of metal sulphides (mainly copper sulphide), causing tarnishing and loss of shine.

All of the above are examples of static electricity. Static electricity is the result of the accumulation of electric charges on the surface of objects. When materials like glass, silk, ebonite, or wool are rubbed together, electrons are transferred, creating a charge imbalance. Similarly, lightning is a large-scale natural discharge of static electricity between clouds and the Earth.

• Glass rod & silk cloth: Positive and negative charges develop.
• Ebonite rod & wool: Negative charge accumulates on ebonite.
• Lightning: Discharge of atmospheric static electricity.

Explanation: Marijuana is a psychoactive drug obtained from the female inflorescence (flowering tops) of the Cannabis sativa plant. It contains the active compound tetrahydrocannabinol (THC), which affects the central nervous system and alters mood and perception.

Explanation: Proteins are complex organic compounds composed of smaller units called amino acids. Each amino acid contains an amino group (–NH₂), which contributes nitrogen to the molecular structure. This makes nitrogen an essential element in all proteins. Carbohydrates and fats lack nitrogen, while only some vitamins contain it.