Sputnik I was the first artificial satellite to orbit the Earth. It was launched by the Soviet Union on October 4, 1957. The successful launch of Sputnik I marked the beginning of the space age and initiated the space race between the USA and the USSR.

• Explorer I: First U.S. satellite, launched in 1958.
• Vanguard I: A U.S. satellite launched later in 1958.
• Discoverer I: Part of an American reconnaissance satellite program (1959).

Explanation: Fire extinguishers commonly used in houses and offices contain water, potassium bicarbonate (KHCO₃), and fluorocarbons. These chemicals help in extinguishing fires by cooling, cutting off oxygen supply, and preventing the spread of flames without leaving harmful residues.

Explanation: RADAR (Radio Detection and Ranging) works by using radio waves to detect and determine the distance, speed, and position of objects such as aircraft, ships, and vehicles. The radar system transmits radio waves, which travel through the air, hit an object, and get reflected back to the radar receiver. By measuring the time delay between transmission and reception, the radar calculates the object's distance and motion. Radio waves are ideal because they can travel long distances, penetrate clouds, and are unaffected by weather conditions.

Explanation: The processes that add carbon dioxide (CO₂) to the carbon cycle on Earth are:

• 1. Volcanic action: Volcanic eruptions release large amounts of CO₂ and other gases from the Earth’s interior into the atmosphere.
• 2. Respiration: All living organisms release CO₂ as a by-product of breaking down glucose during cellular respiration.
• 4. Decay of organic matter: Decomposition of dead plants and animals by microbes produces CO₂ and methane (CH₄).

Photosynthesis (option 3), on the other hand, removes CO₂ from the atmosphere as plants use it to produce glucose and release oxygen.

Explanation: The angle of friction and the angle of repose are equal to each other. The angle of friction is the angle made by the resultant of the limiting friction and normal reaction with the normal force, while the angle of repose is the maximum angle of an inclined plane at which an object just begins to slide. Both represent the same physical condition of impending motion.

Explanation: Bryology is the branch of botany that deals with the study of bryophytes, which include mosses and liverworts. These are small, non-vascular plants that typically grow in moist and shady environments.

Explanation: White blood cells (WBCs), also known as leukocytes, are responsible for producing the immune response in the human body. They defend against infections by attacking bacteria, viruses, and other foreign invaders, helping to maintain the body’s immunity.

Explanation: The age of a tree is determined by counting the annual growth rings (also called annual rings) visible in a cross-section of its trunk. Each ring consists of a light band (spring wood) and a dark band (autumn wood), representing one year of growth. The study of these rings to determine a tree’s age and past climate conditions is known as dendrochronology.