General Science Previous Year Questions (PYQ) with Answers – Page 84

The brain is divided into fore-brain, mid-brain and hind-brain, and the fore-brain is the main thinking part. Its largest portion is the cerebrum, whose folded outer layer holds separate areas for hearing, sight, smell and touch, for reasoning and memory, and for ordering voluntary movement.

It is a reduction division: one parent cell with the full, diploid set gives four cells with half the number of chromosomes, the haploid set.

Malleability is the property by which a metal can be beaten into thin sheets without breaking, which is how aluminium foil and the sheets used in car bodies are made.

A ligament is the connective tissue that joins one bone to another at a joint. It is very elastic and strong, and it holds the bones in place so that a joint can move without the bones slipping apart.

Abscisic acid is the one plant hormone in this list that slows growth instead of speeding it up, which is why it is often called the stress hormone of plants.

Testosterone is made by the Leydig cells of the testes and is the main male sex hormone.

White blood cells are usually about 8 to 20 micrometres across, larger than red cells but not in the range given here.

Use the third equation of motion, which links velocity and distance without needing time: v squared equals u squared plus 2as.

Power is the rate of doing work, so power equals work divided by time. Here the work is 120 J and the time is 3 seconds, which gives 120 divided by 3, that is 40 watts.

The pH is the negative logarithm of the hydrogen ion concentration, so each rise of one unit means the concentration has fallen to one tenth.

Vegetable oils contain unsaturated fatty acids with carbon-carbon double bonds, and when hydrogen is passed through the oil at about 60 degrees Celsius in the presence of finely divided nickel, the double bonds add hydrogen and become saturated, turning the liquid oil into semi-solid vanaspati.

An amphoteric oxide reacts with both acids and bases to give a salt and water. Aluminium oxide dissolves in hydrochloric acid to give aluminium chloride and in sodium hydroxide to give sodium aluminate, so it behaves as a base in one case and as an acid in the other.

Benzene has the formula C6H6 and a ring of six carbon atoms, each carrying one hydrogen. Count the sigma bonds first: six carbon-carbon bonds around the ring and six carbon-hydrogen bonds give twelve sigma bonds.

Ethylene, also called ethene, has the formula C2H4, and its two carbon atoms share two pairs of electrons, which is a carbon-carbon double bond made of one sigma and one pi bond; it is the simplest alkene.

In a double displacement reaction two compounds exchange their ions, so both reactants must be compounds. Here hydrogen and oxygen are elements combining to form a single product, water, which makes it a combination reaction and also a combustion and redox reaction, but certainly not a double displacement.

When a floating body tilts a little, the centre of buoyancy shifts to the centre of the newly displaced water, and the vertical drawn through it cuts the original axis of the body at a point called the metacentre.

John Newlands arranged the fifty-six elements known in 1866 in order of increasing atomic mass, beginning with hydrogen, the lightest, and ending with thorium, the fifty-sixth.

The alkali metals are lithium, sodium, potassium, rubidium, caesium and francium. Each has a single electron in its outermost shell, loses it readily to form a positive ion, and therefore stands in group 1 of the modern periodic table.

The capacity of a shell is given by the formula 2n squared, where n is the number of the shell counted outward from the nucleus.

The Greek philosopher Democritus, working in the fifth century before the common era, argued that matter could be divided only up to a limit, and he called that smallest indivisible particle atomos, from which the word atom comes.