Explanation: Sound travels fastest in steel because it is a solid material where the particles are packed very closely together. Sound waves need a medium to travel, and their speed depends on how quickly vibrations can pass from one particle to another. In solids, particles are tightly bound, so vibrations are transmitted more efficiently. In contrast, sound travels slower in liquids and slowest in gases. It cannot travel through a vacuum because there are no particles to carry the vibrations.

One molecule of a Chlorofluorocarbon (CFC) can destroy up to 1,00,000 molecules of ozone (O₃) in the ozone layer. When CFCs reach the stratosphere, they are broken down by ultraviolet (UV) radiation, releasing chlorine atoms. Each chlorine atom acts as a catalyst in the breakdown of ozone molecules, significantly depleting the protective ozone layer that shields Earth from harmful UV rays.

Other options (for context)

• 10,000: Underestimates the destructive potential of a single CFC molecule.
• 10,00,000: Overestimates the number of ozone molecules destroyed.
• No one of the above: Incorrect — the correct answer is 1,00,000 molecules of ozone.

Explanation: Asbestos is a group of naturally occurring fibrous silicate minerals once widely used in construction and insulation. When inhaled, asbestos fibers accumulate in the lungs and pleura, leading to inflammation and scarring over years. This chronic exposure can cause asbestosis (lung fibrosis) and mesothelioma — a deadly cancer of the membrane lining the lungs (pleura) or abdomen (peritoneum).

Explanation: The incorrect pair is Faraday : Diffusion of gases. The diffusion of gases was studied and explained by Thomas Graham, not by Michael Faraday. Graham’s Law states that the rate of diffusion of a gas is inversely proportional to the square root of its density or molar mass. On the other hand, Michael Faraday is famous for his work on electromagnetism and electrolysis. The other pairs are correctly matched with their discoveries.

The Abacus is considered the first calculating device in human history. It was invented around 2500 BCE and used in ancient civilizations such as China, Egypt, and Mesopotamia. The Abacus consists of beads that slide on rods or wires, representing numbers, and is used to perform basic arithmetic operations like addition, subtraction, multiplication, and division. It laid the foundation for modern computing and calculating tools.

Other options (for context)

• Calculator: A modern electronic device for computation, developed much later.
• Turing machine: A theoretical computational model proposed by Alan Turing in 1936.
• Pascaline: A mechanical calculator invented by Blaise Pascal in 1642, long after the Abacus.

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.

The Stockholm Convention is not associated with the reduction of greenhouse gases. It focuses on eliminating or restricting the production and use of persistent organic pollutants (POPs) — toxic chemicals that remain in the environment for long periods, such as DDT and PCBs. It does not directly address greenhouse gas emissions or climate change.

Other options (for context)

• Kigali Amendment to the Montreal Protocol: Aims to phase down the use of hydrofluorocarbons (HFCs), which are potent greenhouse gases used in refrigerants — hence it helps reduce global warming.
• Kyoto Protocol: An international treaty adopted in 1997 to reduce greenhouse gas emissions by developed countries, directly targeting climate change.

Explanation: The femur is the single bone of the thigh region and extends from the hip joint to the knee joint. It supports the body’s weight during standing, walking, and running. The femur is the longest, heaviest, and strongest bone in the human skeleton. It articulates with the pelvic girdle at its proximal end (head of femur fits into the acetabulum of the pelvis) and with the tibia and patella at the distal end.

Average Length: Approximately 45 cm (about 1/4 of body height).