General Science Previous Year Questions (PYQ) with Answers – Page 16

Sodium is a metal that gives up an electron easily and chlorine is a non-metal that accepts one, so the two form sodium chloride, an ionic compound.

As the body falls its height shrinks, so the potential energy m g h falls, but exactly that much energy reappears as kinetic energy, half m v squared, because the body speeds up.

When enough air reaches the burner, every carbon atom of the fuel is oxidised fully to carbon dioxide and the flame is blue and hot, giving the maximum heat for the gas consumed.

An iron rod is a solid, and the force of attraction between particles is strongest in the solid state. In a solid the particles sit close together in fixed positions and can only vibrate, so a solid keeps its shape, has a definite volume and can hardly be compressed.

Force has to be applied to break the chalk because its particles hold one another together, and that pull is the force of attraction between particles.

This set is wrong because chikungunya is caused by a virus, the chikungunya virus, and not by bacteria. It is spread by Aedes mosquitoes, the same day-biting mosquitoes that carry dengue and Zika, and it causes high fever with severe joint pain.

The lens of the eye is made mostly of water and special proteins called crystallins, packed in a very regular order that keeps the lens clear so light can pass straight through to the retina.

The stapedius, only about 1 millimetre long, is the smallest skeletal muscle in the human body. It lies in the middle ear and is attached to the stapes, which is itself the smallest bone of the body.

Milk of magnesia is a milky white suspension of magnesium hydroxide, Mg(OH)2, in water. It is a mild base, so it neutralises the extra hydrochloric acid in the stomach that causes acidity and heartburn; the reaction gives magnesium chloride and water.

In 1831 the British scientist Michael Faraday showed that a changing magnetic field produces an electric current in a nearby coil.

Calcium oxychloride (CaOCl2) is bleaching powder, and the chlorine it releases removes colour from cotton and linen in the textile industry.

In a metal, the outer electrons of the atoms are not tied to any one atom and drift through the lattice when a voltage is applied, carrying the current.

Adding hydrogen across the double or triple bond of an alkene or alkyne turns it into a saturated alkane; this reaction is called hydrogenation and it needs a catalyst.

In his 1913 model of the atom, Bohr proposed that electrons move in certain fixed orbits, called stationary states, in which they do not radiate energy.

A primary rainbow comes from light that is refracted into a raindrop, reflected once inside it and refracted out again, and it is the brighter, inner bow.

Two trends of the periodic table decide the order. Going down a group, atomic radius increases because each new period adds an electron shell; so sodium, in period 3, is larger than lithium, in period 2, of the same group 1.

A compound microscope uses two converging lenses, the objective and the eyepiece, to give a greatly magnified image of a tiny object.

Antibodies are made by B-lymphocytes, a kind of white blood cell, after they meet a foreign antigen. When a germ or other foreign substance enters the body, B-lymphocytes that recognise its antigen multiply and turn into plasma cells.

In bacteria the DNA is not wrapped around histone proteins as it is in the chromosomes of eukaryotes, so it is called naked DNA.

Newton's law of cooling describes a hot body losing heat to cooler surroundings, which is exactly what a cup of coffee on a table does.