Explanation: Smallpox is a highly contagious and deadly disease caused by the Variola virus. It is characterized by high fever, fatigue, and a distinctive pustular rash on the skin. Smallpox was one of the most devastating diseases in human history, but thanks to the worldwide vaccination campaign led by the World Health Organization (WHO), it was officially eradicated in 1980. The vaccine for smallpox was first developed by Edward Jenner in 1796.

Explanation: An anemometer is a meteorological instrument used to measure wind speed and direction. It is an essential tool in weather stations, aviation, and marine forecasting.

Working Principle: The cup anemometer has three or four cups that rotate with the wind. The rotation speed is proportional to wind velocity. Advanced types also detect wind direction.

Types of Anemometers:

• Cup: Measures wind speed using rotating cups.
• Vane: Measures both speed and direction.
• Hot-wire: Uses heat loss to measure air flow.
• Ultrasonic: Uses sound waves for precise measurement.

Explanation: Photosynthesis is the process by which green plants, algae, and some bacteria use sunlight to convert carbon dioxide (CO₂) and water (H₂O) into glucose (C₆H₁₂O₆) and oxygen (O₂). This process takes place in the chloroplasts of plant cells, which contain the green pigment chlorophyll that captures solar energy.

Chemical Equation:

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Thus, plants are known as autotrophs because they produce their own food using light energy — a process vital for sustaining all life on Earth.

Explanation: The erythrocytes (RBCs) play a crucial role in the circulation of blood by carrying oxygen from the lungs to body tissues and returning carbon dioxide for exhalation. They contain hemoglobin, which binds oxygen and maintains the red color of blood. Circulation itself is driven by the heart and supported by these oxygen-carrying cells.

Explanation: Chlorofluorocarbons (CFCs) are the gases responsible for the depletion of the ozone layer. When released into the atmosphere, CFCs break down under ultraviolet (UV) radiation, releasing chlorine atoms that destroy ozone molecules (O₃), leading to thinning of the ozone layer and increased UV radiation reaching the Earth.

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.

The pale yellow colour of urine is due to the presence of the pigment Urochrome. Urochrome is a waste product formed from the breakdown of hemoglobin in red blood cells. It is produced when hemoglobin is metabolized into urobilin and then excreted through urine. The intensity of the yellow color can vary depending on hydration levels — darker urine indicates dehydration, while pale urine indicates proper hydration.

Other options (for context)

• Urophyll: No such pigment exists in human physiology.
• Chlorophyll: Green pigment found in plants, not in urine.
• Chloroplast: Cell organelle in plants where photosynthesis occurs, not a pigment.

Explanation: Animals that live in or on trees are called arboreal animals. They are adapted to climbing and moving about among branches. Examples include monkeys, squirrels, chameleons, and tree frogs. Their adaptations may include grasping limbs, prehensile tails, claws, or adhesive pads that help them cling to tree surfaces and move efficiently among branches.

Explanation: The pairing Louis Pasteur : Blood groups is not correctly matched. Louis Pasteur is known for his work on pasteurization and germ theory of disease, not for discovering blood groups. The discovery of blood groups was made by Karl Landsteiner in 1900. Other matches are correct.