General Science GK Questions with Answers – Page 25

Birds, blowing dust, rain and wind can all carry the agents of plant disease from one plant to another. Plant pathogens such as fungi, bacteria and viruses cannot move on their own over long distances, so they depend on carriers.

The truth is the reverse: hepatitis B has a safe, effective vaccine, while hepatitis C has none. The hepatitis B vaccine has been in use since the 1980s and is given to newborns in India under the Universal Immunisation Programme, with the first dose soon after birth.

Drug resistance grows in microbes when antibiotics are misused, and both wrong doses and farm use of antibiotics are forms of misuse.

Evaporation is a surface process, so its rate depends on conditions at the surface of the liquid, not on how much liquid there is in total.

Calcium carbonate, CaCO3, is a compound because calcium, carbon and oxygen are chemically combined in it in a fixed ratio.

As one climbs, air pressure falls, so each breath delivers oxygen at a lower partial pressure and less of it passes from the lungs into the blood.

A compound always has a fixed composition by mass, so a variable composition is a property of mixtures, not compounds.

The magnetic force on a moving charge is F = q(v × B), and only an upward field turns a westward-moving positive charge towards the north.

The law of conservation of mass, stated by Antoine Lavoisier in 1789, says that in a chemical reaction mass is neither created nor destroyed.

When copper is left in moist air for a long time, it slowly reacts with oxygen, water vapour and carbon dioxide.

On a hot day the air just above a road or desert sand is much hotter, and so optically rarer, than the air higher up.

At room temperature and normal pressure only two elements are liquids: mercury, a metal, and bromine, a non-metal. Mercury melts at about −39 °C and is used in thermometers and barometers because it stays liquid over a wide range and does not wet glass.

Potassium permanganate, KMnO₄, forms dark purple crystals that contain no water of crystallization; its formula has no attached water molecules.

This statement is wrong because bryophytes, the mosses and liverworts, have no true vascular tissue: they lack xylem to carry water and phloem to carry food.

A reducing agent is the substance that is itself oxidised while it reduces something else. In hydrazine, N₂H₄, nitrogen has an oxidation number of −2; in nitrogen gas, N₂, it is 0.

A p-type semiconductor is made by adding a small amount of a trivalent impurity, such as boron, aluminium, gallium or indium, to pure silicon or germanium.

Friction acts along the surfaces in contact, opposite to the direction of motion, not along the line joining the centres of two bodies, so it is non-central.

An angle of incidence of zero means the ray falls along the normal, that is, perpendicular to the surface. By Snell's law, n₁ sin i = n₂ sin r; if i is zero, sin i is zero, so sin r is also zero and the angle of refraction is zero.

Lime water is a clear solution of calcium hydroxide, Ca(OH)₂. When carbon dioxide is passed through it, insoluble calcium carbonate, CaCO₃, forms as a fine white precipitate, which makes the lime water turn milky.

Bronze is made by mixing copper (Cu) with tin (Sn), usually about nine parts copper to one part tin. Adding tin makes the metal harder, stronger and more resistant to corrosion than pure copper, which is why bronze was used for tools, weapons, bells, coins and statues.