General Science Previous Year Questions (PYQ) with Answers – Page 11

Rutherford's gold foil experiment showed that an atom has a tiny, dense, positively charged centre, which he called the nucleus.

Calcium carbonate, CaCO3, is a compound because calcium, carbon and oxygen are chemically combined in it in a fixed ratio.

A reducing agent is the substance that is itself oxidised while it reduces something else. In hydrazine, N₂H₄, nitrogen has an oxidation number of −2; in nitrogen gas, N₂, it is 0.

Sulphur dissolves completely in carbon disulphide, so the two form a true solution, and a solution is a homogeneous mixture.

That is false: in a physical change the molecules stay the same, and only their arrangement, state or shape alters.

When ice melts it only changes from solid to liquid; the substance is still water, so it is a physical change.

The element with atomic number 11 is sodium, and with one electron in its outermost shell its valency is 1.

Rutherford's model could not explain why the orbiting electrons do not fall into the nucleus. According to classical physics, a charged particle moving in a circular path is accelerating and must keep radiating energy.

There is no compound with the formula 4CaO·SiO₂ in Portland cement; the four main compounds of cement clinker are dicalcium silicate, tricalcium silicate, tricalcium aluminate and tetracalcium aluminoferrite.

Indigestion and heartburn are usually caused by too much acid in the stomach, and an antacid is a mild base that neutralises this extra hydrochloric acid.

Isobars are atoms of different elements that have the same mass number but different atomic numbers. The mass number is the total of protons and neutrons in the nucleus, so isobars have the same number of nucleons arranged differently: more protons and fewer neutrons in one, the reverse in another.

The statement is false because CaSO4·2H2O is gypsum; Plaster of Paris is calcium sulphate hemihydrate, CaSO4·½H2O. When gypsum is heated to about 373 K, it loses three-quarters of its water and becomes Plaster of Paris, a white powder.

Lime water is a clear solution of calcium hydroxide, and carbon dioxide reacts with it to form insoluble calcium carbonate, which turns the solution milky.

Both beams carry conventional current in the same direction, north to south, and parallel currents in the same direction attract each other.

By Ohm's law the heater's resistance is 40 V divided by 2 A, which is 20 ohms, so at 140 V it draws 140 divided by 20, or 7 A. Ohm's law states that, at constant temperature, the current through a conductor is directly proportional to the potential difference across…

In long-sightedness (hypermetropia) the eye cannot see nearby objects clearly because their image is formed behind the retina.

The splitting of white light into its seven component colours by a prism is called dispersion. White light is a mixture of colours, and glass bends each colour by a different amount because its refractive index depends on wavelength.

A refrigerator moves heat from a cold space to a warmer room, which never happens on its own, and the second law explains what it takes to make it happen.

Potassium carbonate comes from a strong base and a weak acid, so statement 1 is wrong, while statements 2 and 3 are right.

The Haber process is exothermic, not endothermic: nitrogen and hydrogen combine to form ammonia and release heat. In the Haber process, N2 + 3H2 ⇌ 2NH3 gives out about 92 kJ for every two moles of ammonia formed.