The Itai-Itai disease is caused by Cadmium (Cd) poisoning. The disease was first identified in Japan, where industrial discharge of cadmium-contaminated water led to severe pollution. People consuming rice grown in this contaminated water suffered from extreme pain in bones and joints, along with kidney damage. The name "Itai-Itai" literally means "ouch-ouch" in Japanese, reflecting the severe pain experienced by victims.

Other options (for context)

• Nickel: Causes dermatitis and allergic reactions but not Itai-Itai disease.
• Chromium: Can cause skin and respiratory problems, not bone-related disorders.
• Mercury: Leads to Minamata disease, not Itai-Itai disease.

Explanation: Penicillin was discovered accidentally by Alexander Fleming in 1928 when he observed that a fungal mold, Penicillium notatum, inhibited the growth of Staphylococcus bacteria in his culture plates. Penicillin became the first antibiotic used to treat bacterial infections and saved millions of lives during World War II. Later, scientists like Howard Florey and Ernst Boris Chain developed methods for its large-scale production.

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.

Explanation: In a healthy adult, the total volume of blood in the body is approximately 7% of body weight. For an average person weighing around 70 kg, this equals about 5 to 5.5 litres of blood. Blood plays a vital role in transporting oxygen, nutrients, hormones, and waste products throughout the body. It also helps regulate temperature and maintain pH balance. The major components of blood are plasma (55%), red blood cells (RBCs), white blood cells (WBCs), and platelets.

Explanation: The King Cobra (Ophiophagus hannah) is the world’s longest venomous snake and the only snake species that builds a nest to lay its eggs. The female collects leaves, twigs, and debris to construct a mound-like nest, usually near dense vegetation or fallen logs. She lays about 20–40 eggs in the nest and guards them aggressively until they hatch, showing remarkable parental care — a rare behavior among reptiles.

Once the eggs are about to hatch, the female leaves the nest to avoid eating her own offspring, as King Cobras are carnivorous and feed mainly on other snakes.

Explanation: Malaria and Trichomoniasis are both protozoan diseases, not bacterial. Malaria is caused by Plasmodium species (transmitted by female Anopheles mosquitoes), while Trichomoniasis is caused by Trichomonas vaginalis, a sexually transmitted protozoan infection. Unlike bacterial diseases, these are treated using antiprotozoal drugs rather than antibiotics.

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.

Explanation: Nuclear fission is the process in which the nucleus of a heavy atom, such as Uranium-235 or Plutonium-239, splits into two or more lighter nuclei when bombarded by a slow-moving neutron. This reaction releases a large amount of energy, along with additional neutrons that can trigger further fission reactions—leading to a chain reaction. This principle is used in nuclear reactors for power generation and in atomic bombs for explosive energy release.