General Science Previous Year Questions (PYQ) with Answers – Page 81

A catalytic poison is a substance that lowers or destroys the activity of a catalyst, usually because it sticks firmly to the active surface and leaves no room for the reactants.

The number of moles is the given mass divided by the molar mass, so 60 grams of helium divided by 4 grams per mole gives 15 moles.

A mole is a count, not a weight: one mole of any element holds 6.022 into 10 to the power 23 atoms, the Avogadro number, whatever the element is.

First find the throwing speed from the height: v squared equals u squared minus 2 g h gives u equal to the square root of 2 into 10 into 80, that is 40 metres per second.

By the work-energy theorem the work done by a force equals the change in kinetic energy, so the work here is half of 4 kilograms times 5 metres per second squared, that is 0.5 into 4 into 25, which gives 50 joules.

A convex mirror bulges towards the viewer and always gives a virtual, erect and diminished image, so whatever your distance from it, your reflection looks smaller than you.

Protein synthesis begins with transcription, in which the message of a gene is copied from DNA into messenger RNA, so the first event is the making of an mRNA copy.

An ordinary filament bulb is filled with a mixture of argon and nitrogen because both are chemically unreactive and will not burn the white-hot tungsten filament.

Bronze is an alloy of copper and tin, usually about 88 per cent copper to 12 per cent tin. Tin makes copper harder and gives it a far better resistance to rust and sea water, which is why bronze is used for statues, temple bells, coins, medals and ship fittings.

The focal length of a mirror does not depend on the medium around it, so a convex mirror of focal length f in air keeps the focal length f inside the liquid.

Phosphorus, sulphur, chlorine and argon all sit in the third period of the periodic table, so their electrons fill the same three shells.

Emerald is the deep green variety of the mineral beryl, a beryllium aluminium silicate, so beryllium is part of its very formula.

Sulfur dioxide is made of one sulfur atom and two oxygen atoms, so its molecular mass is the sum of their atomic masses: 32 plus 2 multiplied by 16, that is 32 plus 32, which gives 64 u. Molecular mass is expressed in unified atomic mass units, written u, and…

Calcium chloride is an ionic compound, so it has a formula unit mass rather than a molecular mass, and the value is found by adding the atomic masses of all the atoms in the formula.

An alkene is an unsaturated hydrocarbon in which two carbon atoms are joined by a double bond, so the carbon-to-carbon double bond is its identity.

Alkanes are saturated hydrocarbons, so every bond between two carbon atoms is a single bond and all the remaining valencies are filled by hydrogen.

The d-block sits in the middle of the periodic table, bridging the s-block on the left and the p-block on the right.

The halogens are placed in Group 17 of the modern periodic table. This family has five members - fluorine, chlorine, bromine, iodine and astatine.

An alkene carries one carbon-to-carbon double bond, and that bond uses up two hydrogen atoms that a saturated chain would have held, so the formula drops from CnH2n+2 to CnH2n. Putting n equal to 2 gives C2H4, ethene, the simplest alkene; n equal to 3 gives C3H6, propene.

Alkanes are saturated hydrocarbons in which carbon atoms are joined only by single bonds, and such a chain carries the largest possible number of hydrogen atoms, given by CnH2n+2.