Explanation: The speed of light is maximum in a vacuum (approximately 3 × 10⁸ m/s) and decreases as it passes through denser media. Among the given options — vacuum, air, water, and glass — light travels slowest in glass because glass has the highest refractive index (around 1.5). The greater the refractive index, the slower the light travels. This slowing down of light causes refraction, or bending of light, when it passes from one medium to another.

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.

Dynamite was invented by Alfred Nobel in 1867. He was a Swedish chemist, engineer, and industrialist who discovered that nitroglycerin could be stabilized by mixing it with an absorbent material like diatomaceous earth, making it safer to handle and transport. This invention revolutionized the mining and construction industries. In his later years, Alfred Nobel established the Nobel Prizes using the wealth he accumulated from his inventions.

Other options (for context)

• J. B. Dunlop: Invented the pneumatic rubber tyre.
• James Simons: A mathematician and hedge fund manager, not an inventor.
• Peter Hargreaves: Not related to any major scientific invention; possibly confused with James Hargreaves, who invented the Spinning Jenny.

Adolf Gaston Eugen Fick, a German physiologist, invented the first successful contact lens in 1888. His design consisted of a glass lens that covered the entire eye, resting on the sclera (the white part of the eye). Though bulky and uncomfortable by today’s standards, it laid the foundation for modern soft and gas-permeable contact lenses used in vision correction and cosmetics.

Other options (for context)

• Enrico Fermi: Known for his work in nuclear physics and development of the first nuclear reactor.
• Sandford Fleming: Introduced the concept of standard time zones.
• Benoit Fourneyron: Invented the water turbine, not related to optics or vision correction.

Explanation: A light year is a unit used to measure stellar or astronomical distances. It is defined as the distance that light travels in one year in a vacuum. Since light moves at a speed of about 3 × 10⁸ m/s, one light year equals approximately 9.46 × 10¹² km. It is commonly used to express distances between stars and galaxies because these distances are too large to be measured in kilometers or miles.

Explanation: The major cause of global warming is the increasing concentration of carbon dioxide (CO₂) in the atmosphere. CO₂ is a greenhouse gas that traps heat radiating from the Earth's surface, preventing it from escaping into space — a phenomenon known as the greenhouse effect. Human activities such as the burning of fossil fuels, deforestation, and industrial emissions have significantly increased CO₂ levels, leading to a rise in the Earth’s average temperature, melting of glaciers, rising sea levels, and climate change.

Explanation: A concave mirror can produce an image that is larger than the object when the object is placed between the mirror’s pole and its focal point. This property makes concave mirrors useful in applications like shaving mirrors and makeup mirrors, where magnified images are needed.

Explanation: The habitat of an organism is its natural living place where it finds food, water, shelter, and mates for reproduction. Examples include a pond for a frog, soil for an earthworm, and forest for a tiger. Each species has a specific habitat suited to its survival needs. The niche, on the other hand, describes the organism’s role or function in that habitat, such as how it obtains food or interacts with others.