General Science GK Questions with Answers – Page 23

Specific heat is a property of the material, not of the size or shape of the particular body. It is the amount of heat needed to raise the temperature of unit mass (1 kg or 1 g) of a substance by one degree.

X-rays have wavelengths of roughly 0.01 to 10 nanometres, and a typical value is about one ångström (1 Å = 10⁻¹⁰ m = 0.1 nm).

Ice is simply water in its solid state, a single compound with the fixed formula H2O, so it is a pure substance, not a mixture.

Vegetable oils are hardened into margarine and vanaspati ghee by hydrogenation. Liquid vegetable oils are unsaturated: their fatty-acid chains contain carbon-carbon double bonds.

This matches the reactivity series, which lists metals from the most to the least reactive. Sodium is near the top: it reacts violently with cold water and is stored under kerosene.

Temporary hardness is caused by the bicarbonates (hydrogencarbonates) of calcium and magnesium dissolved in water. It is called temporary because it can be removed simply by boiling: on heating, the soluble bicarbonates break down into insoluble carbonates, or magnesium hydroxide, which settle out, and carbon dioxide escapes.

Quick lime is calcium oxide (CaO), which contains no carbonate, so it gives no carbon dioxide with an acid. Acids release carbon dioxide only from carbonates and hydrogencarbonates: the general reaction is metal carbonate plus acid gives salt, water and carbon dioxide.

Plaster of Paris is made from gypsum, not from common salt. When gypsum, calcium sulphate dihydrate (CaSO4·2H2O), is heated to about 373 K, it loses part of its water and becomes calcium sulphate hemihydrate (CaSO4·½H2O), which is Plaster of Paris; it sets hard again when mixed with water and is…

Anthracene sublimes on heating, while common salt does not, so heating the mixture separates them. Sublimation is the change of a solid directly into vapour without passing through the liquid state.

A honeybee sting injects methanoic acid, also called formic acid (HCOOH), which causes the burning pain and irritation.

Potassium hydroxide gives potassium soaps, which are softer and milder than sodium soaps. Saponification is the reaction in which an oil or fat is heated with an alkali to give soap, the sodium or potassium salt of a long-chain fatty acid, and glycerol.

Rain water is the purest natural form of water because it is formed by evaporation and condensation, a natural distillation.

Photosynthetic bacteria have no chloroplasts; their pigments sit on infoldings of the cell membrane that form vesicles or sacs, often called chromatophores.

Adipose tissue is a loose connective tissue whose cells, called adipocytes, are built to store fat. Each cell holds a large droplet of fat that pushes the nucleus and cytoplasm to one side.

Germanium is a metalloid, an element whose properties lie between those of metals and non-metals. It is a hard, shiny, grey-white solid like a metal, yet it is brittle and conducts electricity far less well than a metal, which makes it a semiconductor.

This statement is wrong because every photon, whatever its energy, travels in vacuum at the same speed of light, about 3 × 10^8 metres per second.

Temporary hardness is caused by the bicarbonates of magnesium and calcium, Mg(HCO3)2 and Ca(HCO3)2. It is called temporary because simple boiling removes it: on heating, the soluble bicarbonates break down into insoluble carbonate or hydroxide, carbon dioxide and water, and the solid settles out.

The gap between an object and its real image is smallest when the object is placed at 2F, twice the focal length from the lens.

Rutherford's gold foil experiment showed that an atom has a tiny, dense, positively charged centre, which he called the nucleus.

A rod standing upright on one end falls over at the slightest push, because its centre of gravity is high and its base is tiny.