General Science Previous Year Questions (PYQ) with Answers – Page 31

Quick lime is calcium oxide, CaO, and not calcium carbonate, so it is the odd one out. Limestone, chalk and marble are all natural forms of calcium carbonate, CaCO3, differing only in how they were formed and in how hard they are.

Time period is the time taken for one full oscillation, so it is the total time divided by the number of oscillations: 64 divided by 40 gives 1.6 seconds.

Graphite is soft and slippery rather than hard, so this is the statement that is not correct. The difference between the allotropes comes from the way the carbon atoms are joined.

A colloid only looks uniform to the eye; it is in fact a heterogeneous mixture, so this is the statement that is not true.

The statement in the question is Avogadro's law, given by the Italian scientist Amedeo Avogadro in 1811.

A shortage of iodine makes the thyroid gland in the neck swell, a condition called goitre. The thyroid needs iodine to make the hormone thyroxine, and when iodine is short the gland grows larger to trap whatever little is available, so the neck looks visibly swollen.

A block lying quietly on a table is in equilibrium, so the forces on it must add up to zero, but that does not mean there are no forces at all.

This is the statement that is not correct, because water has a much higher surface tension than ethyl alcohol.

A solar cell turns sunlight straight into electricity by the photovoltaic effect at a semiconductor junction, usually of silicon, so nothing inside it turns or slides.

Only a transverse wave can be polarised, so the polarisation of light proves that its vibrations are at right angles to the direction of travel.

Sodium benzoate is the sodium salt of benzoic acid and is the preservative most often added to sauces, salad dressings, jams, pickles and soft drinks.

In humans the digestion of starch begins in the buccal cavity, that is the mouth. The salivary glands pour out about 1.5 litres of saliva a day, and the enzyme in it, salivary amylase or ptyalin, breaks starch into the simpler sugar maltose.

James Chadwick discovered the neutron in 1932 by bombarding beryllium with alpha particles and showing that the radiation produced consisted of neutral particles of nearly the same mass as the proton.

Pressure is the force acting on unit area, that is P equals F divided by A, so for the same force a larger area of contact means smaller pressure.

Atmospheric pressure at sea level is about 1.013 into 10 to the power 5 pascal, which presses with roughly the weight of one kilogram on every square centimetre of our body, so it is very large and not negligible at all.

A floating body is at rest, so the upward buoyant force must exactly balance the downward weight of the object.

Algae belong to Thallophyta, the simplest division of the plant kingdom. Their body is a thallus, which means it is not divided into root, stem and leaf, and they have no vascular tissue.

Moss, or Funaria, and Marchantia, a liverwort, are bryophytes, the group called the amphibians of the plant kingdom because they live on land but need water for reproduction.

The flash and the clap are produced at the same instant by the same discharge.

Leucoplasts are the colourless plastids of plant cells, and each kind is named after what it stores.