General Science GK Questions with Answers – Page 111

In methane the carbon atom is joined to four hydrogen atoms by four single bonds and has no lone pair, so the four bonding pairs push one another as far apart as possible and point to the corners of a regular tetrahedron, with bond angles of about 109.5 degrees.

Rusting is a slow oxidation in which iron combines with oxygen in the presence of moisture to form hydrated iron oxide, the reddish-brown flaky substance we call rust.

Zinc is above hydrogen in the reactivity series, so it displaces hydrogen from a dilute acid: zinc and dilute hydrochloric acid give zinc chloride and hydrogen gas.

A nitrogen atom has five valence electrons and needs three more to complete its octet, so two nitrogen atoms share three pairs of electrons and form a triple bond, written N to N with three lines.

In an ionic or electrovalent bond a metal atom loses one or more electrons to a non-metal atom; the metal becomes a positive ion and the non-metal a negative ion, and the electrostatic attraction between the two holds the compound together, as in sodium chloride and magnesium oxide.

Vegetable oils contain unsaturated fatty acids with carbon-carbon double bonds, and when hydrogen is passed through the oil at about 60 degrees Celsius in the presence of finely divided nickel, the double bonds add hydrogen and become saturated, turning the liquid oil into semi-solid vanaspati.

An amphoteric oxide reacts with both acids and bases to give a salt and water. Aluminium oxide dissolves in hydrochloric acid to give aluminium chloride and in sodium hydroxide to give sodium aluminate, so it behaves as a base in one case and as an acid in the other.

Benzene has the formula C6H6 and a ring of six carbon atoms, each carrying one hydrogen. Count the sigma bonds first: six carbon-carbon bonds around the ring and six carbon-hydrogen bonds give twelve sigma bonds.

Ethylene, also called ethene, has the formula C2H4, and its two carbon atoms share two pairs of electrons, which is a carbon-carbon double bond made of one sigma and one pi bond; it is the simplest alkene.

In a double displacement reaction two compounds exchange their ions, so both reactants must be compounds. Here hydrogen and oxygen are elements combining to form a single product, water, which makes it a combination reaction and also a combustion and redox reaction, but certainly not a double displacement.

Soil acidity is measured on the pH scale, and pH depends on the concentration of hydrogen ions in the soil water.

The carbohydrates in our food are broken down into glucose, and the glucose that the body does not need at once is stored as glycogen, a branched chain of glucose units kept mainly in the liver and the skeletal muscles.

Only a transverse wave can be polarised, so the polarisation of light proves that its vibrations are at right angles to the direction of travel.

A nuclear reactor splits heavy atoms; it burns no fuel, so it releases no carbon dioxide and needs no equipment to cut such emissions.

Bacteria are prokaryotes, so their DNA lies free in the cytoplasm instead of being packed inside a nucleus. The single circular chromosome sits in a region of the cytoplasm called the nucleoid, which has no nuclear membrane around it.

Baking soda is sodium hydrogen carbonate, NaHCO3, a mild base made by the Solvay process from brine, ammonia and carbon dioxide.

Melting means breaking the particles free of the forces holding them in a fixed lattice, so a higher melting point means stronger forces of attraction.

Chadwick discovered the neutron in 1932 and won the Nobel Prize in Physics for it in 1935. He bombarded beryllium with alpha particles and found that the radiation given off was not affected by electric or magnetic fields, yet could knock protons out of paraffin.

Bryophytes live on land but still need water to complete reproduction, so they are called the amphibians of the plant kingdom.

A liquid boils when its vapour pressure equals the pressure of the air pressing on its surface, so lower air pressure means a lower boiling point.