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: A monitor is an output device that displays text, images, and videos generated by the computer. It allows users to visually view the processed data. Common types of monitors include LCD, LED, and OLED screens.

Explanation: Malaria is not caused by a virus; it is caused by a protozoan parasite of the genus Plasmodium. The disease spreads through the bite of an infected female Anopheles mosquito. The parasite enters the human bloodstream, infects liver cells, and then red blood cells, leading to recurring fever, chills, and anemia. In contrast, Smallpox, AIDS, and Flu are all viral diseases caused by the Variola virus, HIV, and Influenza virus respectively.

Carbon dioxide (CO₂) is commonly used as a fire extinguisher gas. It works by displacing oxygen around the fire and forming a blanket of gas that cuts off the oxygen supply, thereby stopping the combustion process. Additionally, CO₂ is non-flammable and leaves no residue, making it ideal for use on electrical and electronic fires where water cannot be used safely.

Other options (for context)

• Nitrogen dioxide (NO₂): A toxic gas, not suitable for firefighting.
• Carbon monoxide (CO): A poisonous gas produced by incomplete combustion, not used in extinguishers.
• Nitrous oxide (N₂O): Commonly known as laughing gas, used as an anesthetic, not a fire suppressant.

Explanation: An artery is a large blood vessel that carries blood away from the heart to various parts of the body. Arteries have thick, elastic walls to withstand high pressure. In contrast, veins carry blood toward the heart, and capillaries are tiny vessels that connect arteries and veins.

Explanation: The terms Dolby B and Dolby C refer to noise reduction circuits used in tape recorders and sound systems. These technologies reduce background hiss and unwanted noise during playback and recording, thereby improving the overall sound quality.

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.

Explanation: The time period of a simple pendulum is given by the formula T = 2π√(L/g), where L is the length of the pendulum and g is the acceleration due to gravity. Since the Moon’s gravity is about 1/6th of Earth’s, the value of g decreases, causing the time period to increase.

Explanation: Human blood is maintained at a slightly alkaline pH of 7.4 (range 7.35–7.45). This balance is vital for the proper functioning of enzymes and biochemical reactions in the body. The buffer systems in blood — primarily the bicarbonate buffer system (H₂CO₃ / HCO₃⁻) — help maintain this stable pH. A small deviation from this range can lead to severe physiological disturbances.

Imbalances:

• Acidosis: pH below 7.35 — causes drowsiness, confusion, and respiratory distress.
• Alkalosis: pH above 7.45 — causes muscle twitching, irritability, and convulsions.