General Science Previous Year Questions (PYQ) with Answers – Page 40

A pH of 11.6 means the soil is strongly alkaline, so it has to be treated with something acidic, and aluminium sulphate is the only acidic compound in the list.

The balanced equation for the complete combustion of glucose is C6H12O6 plus 6O2 gives 6CO2 plus 6H2O, so one mole of glucose needs six moles of oxygen gas.

An alkene has a carbon-carbon double bond, and adding hydrogen across that bond turns it into the corresponding alkane.

Sublimation is the change from solid to vapour without passing through the liquid stage. It happens when particles of the solid gain enough energy to escape straight into the gas phase, and the reverse change, gas to solid, is called deposition.

Muriatic acid is the old trade name for hydrochloric acid, the water solution of hydrogen chloride gas, and the name survives in the market for the crude commercial grade used for cleaning metal and masonry.

All three are mixtures: wood is made of cellulose, lignin, water and resins, air is a mixture of nitrogen, oxygen and other gases, and sand is mostly silica mixed with mineral and shell grains.

Bacteria in the mouth break down leftover food particles and produce acid, not base, so statement d is the incorrect one.

Litmus is a natural indicator obtained from lichens, which are a partnership between an alga and a fungus, and in a neutral solution it shows a purple colour.

Cyclohexane is a closed ring of six carbon atoms joined by single bonds, and each carbon carries two hydrogen atoms, which gives C6H12.

The alkene series begins at two carbon atoms, so its first member is ethene, C2H4, and its second member is propene, C3H6.

Put n equal to 3 in the alkyne general formula CnH2n-2 and the result is C3H4, which is propyne, the second member of the alkyne series.

Carbon is a non-metal, so it does not show metallic character; it neither loses electrons to form positive ions nor shows the lustre and malleability of metals.

The balanced equation is 2FeSO4 → Fe2O3 + SO2 + SO3, so p = 2, q = 1, r = 1 and s = 1.

A medium that holds less water than the cell is a hypertonic medium, so water moves out of the cell by osmosis and the cell shrinks.

Hydrogen is a colourless, odourless and tasteless gas, so none of the colours listed fits it.

A simple pendulum about one metre long completes one full swing in roughly two seconds, and a pendulum of this length is called the seconds pendulum.

In the given equation sodium hydroxide, which is a base, reacts with sulphuric acid to give sodium sulphate and water, and a reaction in which an acid and a base cancel each other to form a salt and water is called neutralisation.

Stomata are the tiny pores on the surface of a leaf through which a plant takes in carbon dioxide and gives out oxygen and water vapour, so the exchange of gases takes place through them.

The object stands between the pole and the focus of the concave mirror, so the image formed is virtual, erect and enlarged, and the magnification is positive.

In the equation given, glucose reacts with oxygen to release carbon dioxide, water and energy, and the breakdown of food inside the cell to release energy is called respiration.