Chemistry Questions and Answers

Answer: A

Boron behaves both as a metal and as a non-metal.

It is a metalloid: it has a lustrous, hard, semiconducting elemental form, yet its oxide \(\mathrm{B_2O_3}\) is acidic and its chemistry is dominated by covalent bonding. Argon is a noble gas, carbon a non-metal and mercury a metal.

Answer: A

Monazite is the ore found in abundance in India.

The beach sands of Kerala, Tamil Nadu and Odisha hold very large monazite deposits, the source of India's thorium and rare-earth reserves. India has to import fluorspar and much of its copper, and its bauxite and magnetite, though substantial, are not exceptional by world standards.

Answer: C

Sodium's symbol is Na.

It comes from the Latin natrium, itself from natron, the naturally occurring sodium carbonate the Egyptians used. Several elements known since antiquity carry Latin symbols in the same way: K for kalium, Fe for ferrum, Ag for argentum.

Answer: B

The other product is 2,2,2-trichloroethanol.

Chloral, \(\mathrm{CCl_3CHO}\), has no \(\alpha\)-hydrogen, so it undergoes the Cannizzaro reaction: \[\mathrm{2\,CCl_3CHO + NaOH \rightarrow CCl_3COONa + CCl_3CH_2OH}\] One molecule is oxidised to the salt of the acid and the other reduced to the primary alcohol. Chloroform would come from the haloform reaction, which is a different process.

Answer: D

All the above describe glycolysis.

It is the first stage in the oxidation of glucose, and it breaks one molecule of glucose down to two of pyruvate: \[\mathrm{C_6H_{12}O_6 + 2NAD^+ + 2ADP + 2P_i \rightarrow 2\,CH_3COCOO^- + 2NADH + 2ATP + 2H^+ + 2H_2O}\] It takes place in the cytoplasm and needs no oxygen, which is why it is common to both aerobic and anaerobic respiration.

Answer: D

Nitrogen has the highest first ionisation potential of the four.

Ionisation energy rises across a period, so oxygen should exceed nitrogen - but nitrogen's \(2p^3\) sub-shell is exactly half filled and therefore unusually stable, while oxygen's \(2p^4\) has one paired orbital whose electron–electron repulsion makes removal easier. So the order is N > O > C > B.

Answer: A

Nitrogen makes air a moderate supporter of combustion.

Being chemically inert under ordinary conditions, it dilutes the oxygen. In pure oxygen things burn fiercely and fires would be uncontrollable; with 78 per cent nitrogen present, combustion proceeds at a manageable rate.

Answer: C

Fluorine is the most electronegative element, at 4.0 on the Pauling scale.

Electronegativity rises across a period as nuclear charge increases, and falls down a group as the atom grows. Fluorine sits at the top right of the reactive elements, so it holds bonding electrons more strongly than anything else; oxygen follows at 3.5.

Answer: B

When a bond forms, the atoms share or transfer electrons.

Transfer gives an ionic bond and sharing a covalent one; either way the atoms reach a more stable electron configuration and the system falls to lower energy. Protons and nuclei are not involved - moving those would be a nuclear process, not a chemical one.

Answer: D

Ammonia is by far the most soluble of these gases in water.

About 700 litres of ammonia dissolve in one litre of water at room temperature, because \(\mathrm{NH_3}\) hydrogen bonds to water and partly reacts with it. Carbon dioxide dissolves to less than one litre per litre, nitrogen barely at all.