Explanation: When a man inside a moving train tosses a coin and it falls behind him, it means the train is moving forward with acceleration. The coin, after being tossed, continues to move with the train’s initial velocity, but since the train speeds up, the coin appears to fall backward relative to the man.

Explanation: The pair Faraday : Diffusion of gases is incorrect. The law of diffusion of gases was given by Thomas Graham, not Michael Faraday. Faraday is known for his work on electromagnetism and electrolysis. The other pairs are correctly matched.

The Big Bang Theory explains the origin of the Universe. According to this theory, the universe began about 13.8 billion years ago from an extremely hot and dense state that expanded rapidly in all directions. This expansion continues even today, leading to the formation of galaxies, stars, planets, and other cosmic structures. The discovery of the cosmic microwave background radiation provides strong evidence supporting the Big Bang Theory.

Other options (for context)

• Origin of Sun: Explained by the Nebular Hypothesis, not the Big Bang Theory.
• Laws of Chemistry: Studied under physical and inorganic chemistry, unrelated to cosmology.
• Laws of History: Concern human civilizations, not the universe’s formation.

Marble is not an element; it is a metamorphic rock composed primarily of calcium carbonate (CaCO₃). It forms when limestone is subjected to high pressure and temperature, causing recrystallization. Being a compound and mixture of minerals, marble does not consist of a single type of atom, unlike elements.

Other options (for context)

• Oxygen (O₂): A chemical element essential for respiration and combustion.
• Nitrogen (N₂): A chemical element that makes up about 78% of Earth’s atmosphere.
• Hydrogen (H₂): The lightest chemical element and the main component of stars.

Explanation: The hard structure of bones and teeth is primarily made of calcium phosphate in the crystalline form of tricalcium phosphate (Ca₃(PO₄)₂). It provides rigidity and strength. In tooth enamel, a small portion is converted into fluorapatite, which makes teeth resistant to bacterial decay.

Explanation: Ecology is a branch of biology that deals with the relationships of living organisms with one another and with their physical surroundings. It examines how organisms adapt to their environment, how energy flows through ecosystems, and how matter cycles within the biosphere. The term “Ecology” was first coined by Ernst Haeckel in 1866.

Explanation: Acid rain is caused by the presence of pollutant gases such as sulphur dioxide (SO₂) and nitrogen oxides (NOₓ) in the atmosphere. These gases are released mainly from burning of coal, oil, and industrial emissions. When they combine with water vapor in the atmosphere, they form sulphuric acid (H₂SO₄) and nitric acid (HNO₃), which fall to the ground as acid rain. It damages soil, plants, aquatic life, and even buildings and monuments made of marble or limestone.

All of the above are examples of static electricity. Static electricity is the result of the accumulation of electric charges on the surface of objects. When materials like glass, silk, ebonite, or wool are rubbed together, electrons are transferred, creating a charge imbalance. Similarly, lightning is a large-scale natural discharge of static electricity between clouds and the Earth.

• Glass rod & silk cloth: Positive and negative charges develop.
• Ebonite rod & wool: Negative charge accumulates on ebonite.
• Lightning: Discharge of atmospheric static electricity.