Science

(b) 3

Aluminium (atomic number 13, configuration 2, 8, 3) has three valence electrons, which it loses to form $\mathrm{Al^{3+}}$. Its valency is therefore 3.

(a) Inflorescence

The edible white "curd" of cauliflower is a compact, immature flowering structure (inflorescence) of many undeveloped flowers.

(d) Cholera

Cholera is caused by Vibrio cholerae, spread through contaminated water and food. Small pox and tuberculosis are airborne, and malaria is spread by the Anopheles mosquito.

(b) F

Electronegativity rises across a period and falls down a group. Fluorine has the highest value on the Pauling scale (4.0), above oxygen (3.5), bromine (2.8) and sodium (0.9).

(b) Sulphuric acid

$\mathrm{H_2SO_4}$ is called the "king of chemicals" or "king of acids" because of its wide industrial use: fertilizers, dyes, explosives, batteries and more.

(c) T and t

Alleles are alternative forms of the same gene, found at the same locus on homologous chromosomes. T (tall) and t (dwarf) are alleles of one gene. TT and Tt are genotypes, not alleles.

(d) 8

Period 3 has 8 elements, Na to Ar, because the 3s and 3p subshells hold 2 + 6 = 8 electrons. Of the options given, 8 is the intended answer. Period 4 is a long period with 18 elements.

(a) gr I & II

The s-block elements have their last electron in an s-orbital ($ns^1$ or $ns^2$). These are the alkali metals (group I) and the alkaline earth metals (group II).

(b) Zn

Zinc is amphoteric. It liberates hydrogen with dilute acid and with hot NaOH:

$\mathrm{Zn + H_2SO_4 \rightarrow ZnSO_4 + H_2\uparrow}$

$\mathrm{Zn + 2NaOH \rightarrow Na_2ZnO_2 + H_2\uparrow}$

Fe does not react with NaOH, and Cu does not displace hydrogen from dilute acids.

(c) $0\ \mathrm{ms^{-1}}$

Sound is a mechanical wave and needs a material medium to travel. In a vacuum there are no particles to carry it, so there is no sound propagation.

(a) Parallel combination

In domestic wiring, appliances are connected in parallel so that each gets the full mains voltage and can be switched on or off independently. If one fails, the others keep working.

(c) 325 K

$T(\mathrm{K}) = t(^\circ\mathrm{C}) + 273 = 52 + 273 = 325\ \mathrm{K}$

(b) 14

The human skull has 22 bones: 8 cranial and 14 facial. The facial bones are the 2 maxillae, 2 zygomatic, 2 nasal, 2 lacrimal, 2 palatine, 2 inferior nasal conchae, the vomer and the mandible.

(d) None

Dmitri Ivanovsky first showed in 1892 that the agent of tobacco mosaic disease passes through a bacteria-proof filter, which is regarded as the discovery of viruses. Ivanovsky is not among the options. Adolf Mayer only described the disease (1886), Beijerinck (1898) named the "contagium vivum fluidum", and Pasteur worked on germ theory and vaccines.

(c) Parabolic mirror

A lamp placed at the focus of a parabolic mirror gives a strong, parallel beam of light, which is why it is used in searchlights and headlights. A spherical concave mirror gives a parallel beam only for a small aperture.

(c) 13.3 m

Apparent depth = real depth / $n$, so with $n = \tfrac{4}{3}$ for water:

$\text{Real depth} = n \times \text{apparent depth} = \frac{4}{3}\times 10 \approx 13.3\ \mathrm{m}$

(b) Sea cucumber

A water vascular system is a feature of phylum Echinodermata (starfish, sea urchin, sea cucumber), used for locomotion, feeding and respiration. Silverfish is an insect, sea anemone is a cnidarian and Sycon is a sponge.

(c) Agaricus bispora

Agaricus bisporus is the common button mushroom, which is edible and widely cultivated. Amanita muscaria (fly agaric) is poisonous, so the "all of the above" option is wrong.

(a) angle of incidence

For a thin prism, with small angles of incidence and prism angle $A$, the deviation is

$\delta = (\mu - 1)A$

It depends on the prism angle and refractive index, but is practically independent of the angle of incidence.

(c) Carbon dioxide

$\mathrm{CO_2}$ is an acidic oxide. It dissolves in water to form carbonic acid:

$\mathrm{CO_2 + H_2O \rightarrow H_2CO_3}$

Ammonia is basic, and hydrogen and nitrogen are neutral.

(a) 125 m

For a stone dropped from rest, $u = 0$:

$h = ut + \tfrac{1}{2}gt^2 = \tfrac{1}{2}(10)(5)^2 = 125\ \mathrm{m}$

(a) 2.42

Diamond has a refractive index of about 2.42, which is very high. This gives a small critical angle (about $24^\circ$) and causes its brilliance through total internal reflection.

(b) Wrought iron

The carbon content of the forms of iron is:

• wrought iron: about 0.05 to 0.25%
• steel: 0.25 to 2%
• cast iron: 2 to 4.5%

Wrought iron has the lowest carbon percentage. Stainless steel is steel alloyed with chromium and nickel and has a low but not the lowest carbon content.

(a) Continuous lever

A wheel and axle acts as a continuously rotating lever. The radius of the wheel is the effort arm and the radius of the axle is the load arm, so

$\mathrm{MA} = \frac{R}{r}$

(c) $\mathrm{SnCl_4}$

A Lewis acid is an electron-pair acceptor. $\mathrm{SnCl_4}$ can accept electron pairs into its vacant d-orbitals. $\mathrm{NH_3}$, $\mathrm{CN^-}$ and $\mathrm{OH^-}$ all have lone pairs to donate, so they are Lewis bases.

(c) Phyllotaxy

Phyllotaxy is the arrangement of leaves on the stem or branch. Anthotaxy is the arrangement of flowers on the axis (inflorescence), and aestivation is the arrangement of floral parts in a bud.

(d) Bauxite

Bauxite ($Al_2O_3\cdot 2H_2O$) is the ore of aluminium. Hematite ($Fe_2O_3$), magnetite ($Fe_3O_4$) and limonite ($2Fe_2O_3\cdot 3H_2O$) are all ores of iron.

(c) Hydrogen

Hydrogen has atomic number 1 and atomic mass about 1 u, the lowest of all elements (helium is 4 u, lithium 7 u, nitrogen 14 u).

(a) 273 K

The triple point of water, where ice, liquid water and vapour coexist in equilibrium, is $273.16\ \text{K}$ (0.01 °C) at 611.7 Pa, i.e. about 273 K.

(b) Silver

Silver has the highest electrical conductivity of all metals (about $6.3\times10^{7}\ \text{S/m}$), higher than copper, gold and aluminium. Copper is used in wires because it is far cheaper.

(c) Pituitary

Oxytocin is made in the hypothalamus and released from the posterior pituitary. It causes uterine contractions during childbirth and milk ejection during suckling.

(c) Plutonium

Plutonium is an extremely toxic radioactive element. It is an alpha emitter, and tiny amounts inhaled or ingested concentrate in the lungs, liver and bones and cause cancer and organ damage. It is usually called the most poisonous element.

(a) Generic and specific name

In binomial nomenclature (Carolus Linnaeus), each organism has a two-part scientific name: the genus (generic) name and the species (specific) name, e.g. Homo sapiens.

(a) glycogen

Fungi store food as glycogen and oils (fat globules), not starch. Starch is the reserve food of green plants and algae.

(d) Vit. K

Vitamin K is needed by the liver to make prothrombin and other clotting factors. Its deficiency causes delayed blood clotting and excessive bleeding.

(a) Phycology

Phycology (algology) is the study of algae. Mycology is the study of fungi, dendrology the study of trees, and virology the study of viruses.

(b) shorter

Atmospheric refraction bends sunlight so that the Sun is seen a few minutes before it actually rises and after it actually sets. Scattering also keeps the sky bright for a while after sunset (twilight). Without an atmosphere, there would be no refraction, so sunrise would come later and sunset earlier, and the day would be shorter.

(a) Mendel

Gregor Johann Mendel, through his pea-plant hybridisation experiments, discovered the laws of inheritance and is called the father of genetics.

(d) Inertia

Inertia is the property of matter to resist a change in its state of rest or motion; it depends on mass and is not an effect of gravity. The atmosphere being held on a planet, tides (due to the Moon and Sun) and the solar system being bound together are all effects of gravity.

70 Hz, which is not among the given options.

Using $v = f\lambda$:

$f = \frac{v}{\lambda} = \frac{350}{5} = 70\ \text{Hz}$

None of (a) 50 Hz, (b) 60 Hz, (c) 65 Hz or (d) 75 Hz equals 70 Hz, so the question has a misprint in its data or options. The nearest option is (d) 75 Hz, but the correct value is 70 Hz.

(b) Sodium lauryl sulphate

A detergent is a synthetic cleansing agent, usually the sodium salt of an alkyl sulphonic or sulphuric acid, e.g. sodium lauryl sulphate $CH_3(CH_2)_{11}OSO_3^-Na^+$. Sodium stearate and sodium palmitate are soaps (sodium salts of fatty acids).

(b) Copper Pyrite

Copper pyrite (chalcopyrite, $CuFeS_2$) is the chief ore of copper. Galena (PbS) is the ore of lead, so (a) is wrong.

(c) convex mirror

A convex mirror diverges the reflected rays and always forms a virtual, erect, diminished image, so it covers a much wider area than a plane or concave mirror. This is why it is used as a rear-view mirror in vehicles.

(b) $(2mE)^{1/2}$

Kinetic energy $E = \frac{1}{2}mv^2$ and momentum $p = mv$. Then

$E = \frac{p^2}{2m} \;\Rightarrow\; p = \sqrt{2mE} = (2mE)^{1/2}$

(c) bryophytes

Bryophytes (mosses and liverworts) are called the amphibians of the plant kingdom. They live on land but need water for fertilisation, because the male gametes swim to the egg.