Chemistry Questions and Answers

Answer: C

Pteridophyta have specialised conducting tissue for water.

Ferns and their relatives are the simplest plants with true xylem and phloem, which is why they are called the first vascular plants. Thallophytes and bryophytes have no such tissue and so must stay small and close to moisture; fungi are not plants at all.

Answer: D

The height of the plant is not a criterion for classification.

Classification rests on fundamental characters that reflect evolutionary relationship - the presence of a membrane-bound nucleus, the mode of nutrition, the basic body design. Height varies with age, soil and climate within a single species, so it carries no taxonomic information.

Answer: D

Living in a large and well furnished house is not important for health.

Health depends on clean surroundings, adequate food and income, and social equality and harmony, which determine whether a person can actually obtain those things. The size or furnishing of a house adds comfort but not health.

Answer: C

The ozone layer is depleted by man-made compounds containing both fluorine and chlorine.

Chlorofluorocarbons drift up to the stratosphere, where ultraviolet light frees a chlorine atom that then destroys ozone catalytically: \[\mathrm{Cl + O_3 \rightarrow ClO + O_2},\qquad \mathrm{ClO + O \rightarrow Cl + O_2}\] One chlorine atom can destroy tens of thousands of ozone molecules before it is removed.

Answer: D

All of the above are necessary.

Food security has three components: availability, meaning enough food is produced and stored; accessibility, meaning it can physically reach people; and affordability, meaning they have the money to buy it. A shortfall in any one leaves people hungry even when the other two are met.

Answer: C

Iron is not supplied by ordinary fertilisers.

Fertilisers supply the three macronutrients - nitrogen, phosphorus and potassium, the N-P-K of the label - because plants need them in quantity. Iron is a micronutrient, needed in traces and usually present in the soil already; manures supply it when it is lacking.

Answer: C

Silver iodide is used to produce artificial rain.

Its crystal lattice closely resembles that of ice, so supercooled droplets in a cloud freeze on it and grow heavy enough to fall. It is dispersed from aircraft or fired from the ground into a cloud that already holds enough moisture.

Answer: B

Homonuclear molecules contain a covalent bond.

Both atoms are of the same element, so their electronegativities are identical and neither can draw the shared pair towards itself. The bond is therefore purely covalent and non-polar, as in \(\mathrm{H_2}\), \(\mathrm{N_2}\) and \(\mathrm{Cl_2}\).

Answer: C

John Dalton proposed the first atomic theory, in 1808.

His postulates were that matter consists of indivisible atoms, that all atoms of an element are alike in mass and properties, and that compounds form when atoms combine in fixed small whole-number ratios. The theory accounted at once for the laws of conservation of mass and of definite and multiple proportions.