General Science Mixed Quiz: Set 146

Lead nitrate breaks down only when it is heated strongly, so the reaction absorbs heat and is endothermic. On heating, lead nitrate gives lead oxide, brown fumes of nitrogen dioxide and oxygen: 2Pb(NO3)2 → 2PbO + 4NO2 + O2.

Speleology is the exploration and scientific study of caves, their formation, the limestone features such as stalactites and stalagmites that develop in them, and the animal life adapted to permanent darkness.

Hydrogen adds across the carbon–carbon double bonds of the oil. Vegetable oils are unsaturated: their fatty acid chains contain C=C double bonds, which keep them liquid.

Each kidney contains about a million nephrons, and each nephron consists of a Bowman's capsule enclosing a knot of capillaries called the glomerulus, followed by a tubule in which useful substances are reabsorbed; together they filter the blood and form urine.

Myopia is short-sightedness: near objects look sharp but distant ones look blurred. In a myopic eye the eyeball is too long or the eye lens is too curved, so light from a distant object comes to a focus in front of the retina instead of on it.

A p-type semiconductor is made by adding a trivalent impurity such as boron, aluminium, gallium or indium.

A gamma ray is a photon of energy with no mass and no charge, so emitting it leaves the count of protons and neutrons unchanged.

Teflon is polytetrafluoroethene, made by the addition polymerisation of tetrafluoroethene. The fluorine atoms shield the carbon chain so completely that the surface is chemically inert, water repellent and almost frictionless, and it holds its properties to high temperature, which is why it coats frying pans and is used for gaskets…

When natural gas or heavy oil burns with too little air, the carbon cannot all turn into carbon dioxide and separates as a very fine black soot, which is collected as carbon black.

A species is a group of organisms that resemble one another in all essential characters and that can interbreed to produce fertile offspring; it is the smallest and the basic unit of classification, and all higher ranks are built by grouping species together.

Nereis, the sandworm, moves with parapodia, paired fleshy flaps on the sides of its body segments, not with pseudopodia. Nereis is a marine annelid.

It is a thin, strap-like muscle that runs across the front of the thigh from the hip bone to the inner side of the knee, and because it crosses two joints it is the longest muscle of the human body; it helps in bending the hip and the knee and…

Moringa is not a legume and tamarind is not native to South Asia, so statements 1 and 2 are false.

The correct answer is B, the Leydig or interstitial cells, which lie in the spaces between the seminiferous tubules of the testis and secrete androgens, chiefly testosterone, under the influence of luteinising hormone from the anterior pituitary.

Nitrogen and oxygen combine only when a lot of energy is supplied. The nitrogen molecule is held by a very strong triple bond, so breaking it takes much energy, and the reaction N₂ + O₂ → 2NO absorbs heat.

The velocity ratio of a pulley system is the distance moved by the effort divided by the distance moved by the load, so it is 12 divided by 3, that is 4.

X-rays are not used in radar; radar works with microwaves, which have wavelengths of a few centimetres. X-rays lie between ultraviolet rays and gamma rays in the electromagnetic spectrum, with wavelengths from about 10 nm down to 0.01 nm, so about 1 Å (0.1 nm) is typical.

Mechanical advantage is defined as the load divided by the effort, so the load is the mechanical advantage multiplied by the effort, that is three multiplied by fifteen, which gives forty-five units.

In an ion exchange plant the water passes through a cation resin, which takes up the calcium and magnesium ions, and then through an anion resin, which takes up the sulphate, chloride and bicarbonate ions; because the hardness-causing ions are actually taken out of the water, the hardness can be…

At a fixed speed v, centripetal acceleration equals v²/r, so a larger radius gives a smaller acceleration. An object moving in a circle at constant speed is still accelerating, because its direction keeps changing.