Explanation: The gas used for artificial ripening of green fruits is ethylene (C₂H₄). Ethylene is a natural plant hormone that regulates fruit ripening by stimulating the conversion of starches into sugars, making the fruit softer and sweeter. In artificial ripening, ethylene gas is introduced in controlled amounts to uniformly ripen fruits such as bananas, mangoes, and tomatoes. However, the use of harmful chemicals like calcium carbide for ripening is banned because it produces toxic substances like acetylene.

Velocity is a vector quantity because it has both magnitude and direction. It represents the rate of change of displacement of an object. Unlike speed, which only tells how fast an object is moving, velocity also indicates the direction of motion.

Other options (for context)

• Mass: A scalar quantity — it has magnitude only, no direction.
• Volume: Scalar — represents space occupied by matter, without direction.
• Speed: Scalar — measures how fast an object moves but not in which direction.

Explanation: A sphygmomanometer is a medical instrument used to measure blood pressure. It consists of an inflatable cuff, a mercury or aneroid gauge, and a bulb for inflation. The cuff is wrapped around the upper arm and inflated to temporarily stop blood flow. As pressure is slowly released, readings are taken for systolic (maximum) and diastolic (minimum) pressure. Normal blood pressure for a healthy adult is about 120/80 mmHg.

Explanation: The rarest blood type in the world is AB⁻ (AB negative). It is found in less than 1% of the global population. People with AB⁻ blood can receive red blood cells from all Rh-negative blood types, but they can donate only to other AB individuals.

Explanation: A barometer is an instrument used primarily for measuring atmospheric pressure. It helps in weather forecasting and determining altitudes (since atmospheric pressure decreases with height). A mercury barometer consists of a glass tube filled with mercury inverted in a mercury reservoir. When air pressure changes, the height of the mercury column changes accordingly. However, a barometer cannot measure the density of a liquid — that function is performed by a hydrometer.

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.

Explanation: The flow of electrons through a metallic wire constitutes an electric current. In metals, free electrons move from the negative terminal to the positive terminal of a power source, while the conventional direction of current is taken as opposite — from positive to negative.

Explanation: When a ship floats on water, it displaces a volume of water whose mass is equal to the mass of the ship. This is in accordance with Archimedes’ Principle, which states that an object floats when the buoyant force (equal to the weight of displaced fluid) balances its own weight.

Explanation: Fibrinogen is a soluble plasma protein produced by the liver. During blood clotting, it is converted into insoluble fibrin threads by the enzyme thrombin. These fibrin threads form a mesh that traps red blood cells and platelets, creating a stable clot to stop bleeding. This process prevents excessive blood loss during injury and is regulated by clotting factors and platelets.

Simplified Reaction:

Fibrinogen → (Thrombin) → Fibrin → Blood Clot