Explanation: The HIV (Human Immunodeficiency Virus) primarily attacks the lymphocytes, especially the CD4⁺ T-helper cells of the immune system. This weakens the body’s defense mechanism, making it vulnerable to various infections and diseases, eventually leading to AIDS (Acquired Immunodeficiency Syndrome).

Explanation: When a bus starts suddenly, the passengers tend to lean backward due to the inertia of rest. Inertia is the tendency of a body to resist any change in its state of motion or rest. The lower part of the passenger’s body moves forward with the bus as it starts, but the upper part of the body tends to remain at rest momentarily. This makes the passenger appear to fall backward relative to the bus. It is a clear example of Newton’s First Law of Motion.

Explanation: Electrons are negatively charged particles that revolve around the nucleus in fixed paths called orbits or shells. The nucleus contains positively charged protons and neutral neutrons, and most of the atom’s mass is concentrated in the nucleus.

Hepatitis is a disease that primarily affects the liver. It is characterized by inflammation of the liver tissues and can be caused by viral infections (such as Hepatitis A, B, C, D, and E viruses), excessive alcohol consumption, toxins, or autoimmune conditions. Symptoms include jaundice (yellowing of the skin and eyes), fatigue, nausea, and abdominal pain. Severe or chronic hepatitis can lead to liver failure or cirrhosis if left untreated.

Other options (for context)

• Pancreas: Affected by diseases like pancreatitis or diabetes, not hepatitis.
• Spleen: Involved in blood filtration and immunity, not affected by hepatitis.
• Small intestine: Responsible for digestion and absorption of food, not linked to hepatitis.

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: Opium is obtained from the latex present in the unripe capsule of the poppy plant (Papaver somniferum). The latex is collected by making incisions on the capsule, and after drying, it forms raw opium, which contains alkaloids like morphine and codeine.

Explanation: ELISA stands for Enzyme-linked immunosorbent assay. It is a biochemical test used to detect and measure antibodies, antigens, proteins, or hormones in a sample. The method relies on an enzyme-linked antigen or antibody and a color change to indicate a positive reaction.