General Science GK Questions with Answers – Page 57

Urea is the form in which the body gets rid of the nitrogen left over when amino acids from proteins are broken down.

A temperature in kelvin is the Celsius temperature plus 273 (more exactly 273.15). The Kelvin and Celsius scales have degrees of the same size, so a change of 1 °C equals a change of 1 K; only their zero points differ.

Common fertilisers supply nitrogen, phosphorus and potassium (NPK); iron is a micronutrient that is usually not part of them. Plants need nitrogen, phosphorus and potassium in large amounts, so these are called primary macronutrients, and fertilisers such as urea, DAP, MOP and NPK mixtures are made to supply them.

Litmus is a natural dye extracted from certain lichens, especially species of Roccella. A lichen is a partnership between a fungus and an alga (or a cyanobacterium): the alga makes food by photosynthesis, while the fungus gives shelter and absorbs water and minerals.

An ammeter measures the electric current flowing in a circuit, in amperes. An ammeter is always connected in series with the part of the circuit whose current is to be measured, so that the whole current passes through it.

If you hold a current-carrying straight wire in your right hand with the thumb pointing along the current, your curled fingers show the direction of the magnetic field lines around it.

Potassium and barium exchange their partner ions: K₂SO₄ and BaCl₂ swap ions to give KCl and BaSO₄. In a double displacement reaction two compounds exchange ions.

Statements 1 and 2 are correct; statement 3 is wrong because zinc is more reactive than iron.

Too little fluoride weakens tooth enamel and makes teeth prone to decay, known as dental caries. Fluoride becomes part of the enamel as fluorapatite, which resists the acids made by mouth bacteria from sugars.

Quartz is crystalline silicon dioxide (SiO₂), an electrical insulator, not a semiconductor. A semiconductor has a conductivity between that of a conductor and an insulator, and its conductivity rises with temperature or when impurities are added (doping).

With equal length and area, the wire of lower conductivity, aluminium, has the higher resistance. Resistance is R = ρl/A, where ρ is resistivity, and resistivity is the reciprocal of conductivity (ρ = 1/σ).

A candle gives light by burning wax, so it converts chemical energy, not electrical energy, into light and heat. In a burning candle the wax vapour combines with oxygen in the air; the chemical energy stored in the wax is released as heat and light.

The black layer on old silver is silver sulphide (Ag₂S). Air contains traces of sulphur compounds, mainly hydrogen sulphide (H₂S) from burning fuels and decaying matter.

Bauxite, a hydrated aluminium oxide (Al₂O₃·2H₂O), is the main ore from which aluminium is extracted. Bauxite is first purified into alumina (aluminium oxide) by the Bayer process.

A guard tube is filled with anhydrous calcium chloride, which absorbs moisture and keeps the hydrogen chloride gas dry. In the school experiment, hydrogen chloride gas is made by heating sodium chloride with concentrated sulphuric acid, and the gas is passed through a guard tube containing calcium chloride.

The gastric glands in the stomach wall secrete hydrochloric acid, the only mineral (inorganic) acid among the options. Hydrochloric acid (HCl) makes the stomach strongly acidic, with a pH of about 1.5 to 3.5.

Pitch is the way our ear senses the frequency of a sound: the higher the frequency, the higher the pitch.

A rainbow forms only because sunlight is refracted, dispersed and internally reflected inside raindrops. When sunlight enters a water droplet it is refracted and split into its colours (dispersion), because each colour bends by a different amount.

Both a plane mirror and a convex mirror always form an erect, virtual image, whatever the distance of the object.

Iron is a transition (d-block) element, and such elements can show more than one oxidation state. In transition metals the energies of the outer s electrons and the inner d electrons are very close, so atoms can lose different numbers of electrons.