General Science Questions and Answers

Answer: B

Protons and neutrons are held together in the nucleus by the strong nuclear force, carried by exchange particles - mesons in the older description, gluons in the modern one.

It is about a hundred times stronger than the electrostatic repulsion between protons, but acts only over about 10⁻¹⁵ m, which is why very large nuclei become unstable.

Answer: C

Correct answer: Newton

One newton is the force that gives a mass of one kilogram an acceleration of one metre per second squared. The joule is the unit of energy, the watt of power and the pascal of pressure.

Answer: D

Green plants need all three - water, sunlight and carbon dioxide - to make sugar:

\[ \mathrm{6CO_2 + 6H_2O \xrightarrow{light} C_6H_{12}O_6 + 6O_2} \]

Water is taken up by the roots, carbon dioxide enters through the stomata, and sunlight supplies the energy, captured by chlorophyll.

Answer: A

Mercury forms amalgams. An amalgam is simply an alloy of mercury with another metal, and mercury will dissolve gold, silver, zinc, sodium and many others at room temperature.

Dental amalgam is mercury with silver and tin; extracting gold by amalgamation exploits the same property.

Answer: C

The banyan sends down aerial roots from its branches, which thicken into pillar-like prop roots when they reach the ground.

A single tree can spread this way over acres. The Great Banyan at Kolkata's botanical garden has more than 3,000 such prop roots and covers about 1.5 hectares.

Answer: B

The mushroom cannot make its own food. It is a fungus and has no chlorophyll, so it lives as a saprophyte, absorbing nutrients from dead organic matter.

Algae, carrot and cabbage all photosynthesise; the carrot's root is a store filled by leaves above ground.

Answer: A

Newton's first law is the law of inertia: a body remains at rest or in uniform motion in a straight line unless acted on by an external force.

Inertia is the property the law describes - the resistance of matter to any change in its state of motion - and it is measured by the body's mass.

Answer: D

Washing soda is hydrated sodium carbonate, Na₂CO₃·10H₂O.

It softens water by precipitating the calcium and magnesium as carbonates, so soap can lather. Baking soda is a different compound, sodium bicarbonate.

Answer: B

Stainless steel is an alloy, and an alloy is a homogeneous mixture - iron with about 11 per cent chromium and often nickel, mixed uniformly at the atomic level.

It is not a compound, because the constituents are not combined in a fixed proportion and can be varied continuously. The chromium forms an invisible oxide film that makes the steel stainless.

Answer: B

Soap is a mixture of sodium or potassium salts of monocarboxylic acids - the long-chain fatty acids such as stearic, palmitic and oleic acid, each with a single -COOH group.

Their salts have one ionic head on a long hydrocarbon tail, which is exactly the structure needed to lift grease into water.