Science

(d) Double displacement reaction

In an acid-base (neutralisation) reaction the ions exchange partners, e.g. $\text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O}$.

(b) Concave lens

A person who cannot see distant objects clearly has myopia (short-sightedness). The image forms in front of the retina. A concave (diverging) lens spreads the rays before they enter the eye, so the image falls on the retina.

(a) Volant

Volant animals are adapted for aerial life and flight, such as birds and bats. Aquatic animals live in water, arboreal animals live on trees and cursorial animals are adapted for running.

(b) Heart muscles

The coronary arteries branch from the aorta just above the aortic valve. They supply oxygenated blood to the cardiac muscle (myocardium) itself.

(a) A.G. Tansley

The term "ecosystem" was coined by the British ecologist A.G. Tansley in 1935. E.P. Odum is called the father of modern ecology, and Haeckel coined the word "ecology".

(b) To make body light

Pneumatic bones of birds are hollow and filled with air sacs. This reduces the body weight and so helps flight.

(b) To make body light

Pneumatic bones are hollow and filled with air sacs connected to the lungs. They reduce body weight, which helps flight.

(d) Work, energy and power are vector quantities

This statement is incorrect. Work, energy and power are all scalar quantities. The other statements are correct: work can be positive, negative or zero, kinetic and potential energy together make up mechanical energy, and power is the rate of doing work.

(d) Work, energy and power are vector quantities

This statement is incorrect: work, energy and power are scalar quantities, since they have magnitude only. The other statements are correct. Work can be positive, negative or zero, kinetic and potential energy together make up mechanical energy, and power is the rate of doing work.

(d) Work, energy and power are vector quantities

This is incorrect because work, energy and power are scalar quantities. The other statements are true.

Use $N = n \times N_A$ with $N_A = 6.022\times10^{23}\ \text{mol}^{-1}$, and $n = \dfrac{\text{mass}}{\text{molar mass}}$.

(a) 0.25 mole of oxygen ($\text{O}_2$)

Molecules $= 0.25 \times 6.022\times10^{23} = 1.5055\times10^{23}$

Atoms $= 2 \times 1.5055\times10^{23} = 3.011\times10^{23}$

(b) 0.7 g of nitrogen ($\text{N}_2$, molar mass 28 g/mol)

$n = \frac{0.7}{28} = 0.025\ \text{mol}$

Molecules $= 0.025 \times 6.022\times10^{23} = 1.5055\times10^{22}$

Atoms $= 2 \times 1.5055\times10^{22} = 3.011\times10^{22}$

(c) 5.3 g of $\text{Na}_2\text{CO}_3$ (molar mass $2(23)+12+3(16) = 106$ g/mol)

$n = \frac{5.3}{106} = 0.05\ \text{mol}$

Molecules (formula units) $= 0.05 \times 6.022\times10^{23} = 3.011\times10^{22}$

Each unit has $2+1+3 = 6$ atoms, so atoms $= 6 \times 3.011\times10^{22} = 1.807\times10^{23}$

(d) 52 g of He (molar mass 4 g/mol, monatomic)

$n = \frac{52}{4} = 13\ \text{mol}$

Atoms $= 13 \times 6.022\times10^{23} = 7.83\times10^{24}$

Since helium is monatomic, molecules $=$ atoms $= 7.83\times10^{24}$.

(d) all of those

Cytochromes are heme-containing electron-carrier proteins. They occur in the plasma membrane of aerobic bacteria, in the thylakoid membranes of chloroplasts (photosynthetic electron transport) and in the inner mitochondrial membrane (respiratory chain).

(b) K

The kelvin (K) is the SI unit of thermodynamic temperature. Celsius and Fahrenheit are not SI units.

(a) Yellow

Zinc chromate ($\text{ZnCrO}_4$) is a yellow pigment, used in anticorrosive primers.

(c) glucose + galactose

Lactose (milk sugar) is a disaccharide made of $\beta$-D-galactose and $\beta$-D-glucose joined by a $\beta(1\to4)$ glycosidic bond.

(a) Work and moment of force

Work $=$ force $\times$ distance has dimension $[ML^2T^{-2}]$. Moment of force $=$ force $\times$ perpendicular distance has the same dimension $[ML^2T^{-2}]$.

Torque ($ML^2T^{-2}$) and force ($MLT^{-2}$) differ, and velocity ($LT^{-1}$) differs from velocity gradient ($T^{-1}$), so (b), (c) and (d) are wrong.

(a) Linear momentum

Since $\vec F_{ext} = \dfrac{d\vec p}{dt}$, if the external force is zero then $\vec p$ is constant. Angular momentum is conserved only when the external torque is zero, which does not follow from zero force alone. Torque and time period are not conserved quantities.

(b) Isobars

Nuclei with the same mass number (same number of nucleons) but different atomic numbers are isobars, e.g. $^{40}_{18}\text{Ar}$ and $^{40}_{20}\text{Ca}$. Isotopes have the same $Z$, isotones the same number of neutrons.

(a) 0

Zero group (noble gas) elements have complete outer shells (octet, or duplet for He), so they neither gain, lose nor share electrons and their valency is zero.

(d) velocity

Velocity has both magnitude and direction, so it is a vector. Power, energy and charge have magnitude only and are scalars.

(c) C

"Black lead" is the old name for graphite, a form of carbon (C). It contains no lead (Pb).

(c) phosphorous

Phosphorus promotes early root development and the growth of roots and root hairs, which is why phosphatic fertilisers are applied at sowing.

(a) Continuous lever

A wheel and axle works as a lever that rotates continuously about the axle. The radius of the wheel is the effort arm and the radius of the axle is the load arm.

(c) Au

The Latin name of gold is aurum, so its symbol is Au. Ag is silver (argentum), Hg is mercury and W is tungsten.

(a) 49°

The refractive index of ice is about $1.31$. The critical angle is given by

$\sin C = \frac{1}{n} = \frac{1}{1.31} \approx 0.763 \Rightarrow C \approx 49^\circ$

(c) graphite

The "lead" of a pencil is a mixture of graphite and clay. It is not the metal lead (Pb).

(a) 2.42

Diamond has a very high refractive index of 2.42. Its critical angle is only about $24.4^\circ$, which causes total internal reflection and its sparkle.

(b) 47

Silver (Ag) has atomic number 47. Copper is 29, gold is 79 and lead is 82.

(b) Uranium

Of the options, uranium (atomic number 92, atomic mass about 238) is the heaviest atom. Gold is about 197, platinum about 195 and silver about 108. Uranium is also the heaviest naturally occurring element in significant amounts.

(c) right auricle and right ventricle

The tricuspid valve has three flaps and lies between the right atrium (auricle) and the right ventricle. It prevents backflow of blood into the atrium. The bicuspid (mitral) valve is on the left side.

(d) Sulphite

Sulphite ($SO_3^{2-}$) is divalent. Iodide ($I^-$), cyanide ($CN^-$) and bicarbonate ($HCO_3^-$) are all monovalent.

(d) Losing water from it's cells

The annulus is a ring of cells with thickened walls. As the cells lose water by evaporation, tension develops and the annulus bends back and ruptures the sporangium. When the tension is released the annulus snaps forward and flings the spores out.

(b) Anaphase-I

In meiosis I the homologous chromosomes separate and move to opposite poles during anaphase-I (a reductional division). In anaphase-II it is the sister chromatids that separate.

(b) Monocarpic

A monocarpic plant flowers and fruits only once in its life and then dies, for example bamboo and the agave. Annuals complete their life cycle within a year, and perennials flower repeatedly.

(c) Polystyrene

Thermocol is expanded polystyrene, a polymer of styrene, used for packing and insulation.

(d) tetravalent

Carbon has atomic number 6 and electronic configuration 2, 4. It has four valence electrons and forms four covalent bonds, so its valency is 4.

(c) Neopilina

Neopilina is a living fossil mollusc. It shows metameric (segmented) features such as repeated gills and muscles, so it links Annelida and Mollusca. Squid, nautilus and sepia are cephalopods.

(c) Fossorial

Fossorial animals are adapted for digging and living underground, for example moles. Arboreal animals live in trees, cursorial animals run, and pelagic animals live in open water.

(b) O

Oxygen is the most abundant element in the Earth's crust, at about 46% by mass. Silicon is second (about 28%), then aluminium and iron.

(c) Wriggler

The aquatic larva of a mosquito is called a wriggler because of its wriggling movement in water. The pupa is called a tumbler. A maggot is a fly larva, a grub is a beetle larva, and a naiad is a nymph of dragonflies and similar insects.

(b) covalent

Non-metals combine by sharing electrons, which forms covalent bonds. Organic compounds are made of carbon, hydrogen and other non-metals and are held together by covalent bonds. Electrovalent bonds form between metals and non-metals.

(d) 4

The atom has atomic number 20, so its configuration is 2, 8, 8, 2. It has four occupied shells, so it lies in period 4. The element is calcium, in group 2.

(c) Mg, Ca

Magnesium and calcium are both Group 2 elements with two valence electrons, so each loses (or shares) two electrons and has valency 2. Li and Na are monovalent, Al is trivalent and P is trivalent or pentavalent.

(c) 6

A p sub shell has three orbitals ($p_x, p_y, p_z$), and each orbital holds at most two electrons, so it holds $3\times 2 = 6$ electrons.

(d) hydrogen

According to the nebular hypothesis, the solar system condensed from a rotating cloud of gas and dust. That cloud was composed mainly of hydrogen (with some helium), the most abundant elements in the universe.

(b) ZnO

Zinc oxide forms white, woolly flakes when zinc burns in air, so it was called philosopher's wool (or nil album). It is used in ointments and paints.

(d) HNO₂

A coordinate (dative) bond is formed when one atom donates both electrons of the shared pair. In nitrous acid, written H–O–N→O, the nitrogen lone pair is donated to oxygen. MgCl₂ is ionic, and H₂O and O₂ contain only ordinary covalent bonds.

(a) The separation of homologous chromosomes at anaphase-I

Disjunction is the separation of paired homologous chromosomes, which move to opposite poles during anaphase I of meiosis. Loss of a chromosome segment is deletion, and modification of gene action by a non-allelic gene is epistasis.

(b) Peristomium

The first true body segment of an annelid is the peristomium, which bears the mouth. The prostomium is a fleshy lobe in front of the mouth and is not counted as a true segment.

(a) Ionic bond

Metals readily lose electrons and non-metals readily gain them. Electron transfer produces oppositely charged ions held together by electrostatic attraction, for example $\mathrm{Na^+Cl^-}$.

(d) Capsid

The protein coat that surrounds the nucleic acid (DNA or RNA) of a virus is called the capsid. It is made of repeating protein subunits called capsomeres.

(a) Tracheids

Water and minerals move upward through the xylem, whose conducting elements are tracheids and vessels. Companion cells and sieve cells belong to the phloem, which carries food.

(b) myrmecophily

Myrmecophily is the association between ants and plants, as in mango and litchi. The ants gain food or shelter, and they may protect the plant from other insects. Entomophily means pollination by insects.

(c) O₂

A diatomic molecule contains exactly two atoms. O₂ has two atoms of oxygen, whereas H₂O is triatomic. HCl is also diatomic, but O₂ is the standard example of a diatomic molecule of an element.

(d) $104^\circ$F

$F = \frac{9}{5}C + 32 = \frac{9}{5}(40) + 32 = 72 + 32 = 104^\circ\mathrm{F}$

(b) diamond

Diamond is the hardest natural substance. Each carbon atom is bonded to four others in a rigid three-dimensional tetrahedral network. Graphite is soft because its layers slide over each other.

(c) carat

The purity of gold is measured in carats. Pure gold is 24 carat, and 22 carat gold is $\frac{22}{24}\approx 91.7\%$ gold.

(a) Chloroplast

Chloroplasts contain chlorophyll and carry out photosynthesis, converting light energy into chemical energy stored in glucose. Chromoplasts and leucoplasts are plastids that store pigments and food respectively, and "plastid" is only the general class.

(b) 16

The specific heat capacity is given by $c = \dfrac{Q}{m\,\Delta T}$.

$c = \frac{80}{5\times 10} = 1.6\ \mathrm{J\,kg^{-1}K^{-1}}$

None of the options equals 1.6. Option (b) 16 is the nearest and is the value obtained if the temperature rise were $1^\circ$C ($80/5 = 16$), so it is the intended choice.

(c) Ethyl alcohol

Ethanol ($\mathrm{C_2H_5OH}$) is the alcohol present in alcoholic drinks. Methyl alcohol is highly poisonous (it causes blindness and death), and isopropyl alcohol is used as an antiseptic and solvent, not for drinking.

(d) Ceramics

Porcelain is a ceramic. It is made by firing clay (kaolin), feldspar and quartz at high temperature, and it is used in crockery, tiles and insulators.

(b) larger friction

Small steps keep the legs nearly vertical, so the backward push on the ice is small compared with the normal force. The friction needed to prevent slipping is therefore smaller than the limiting friction, and the walker does not slip.

(d) Height, density, acceleration due to gravity

The pressure at depth $h$ in a liquid of density $\rho$ is $P=h\rho g$, so it depends on height (depth), density and $g$.

(d) Thermal capacity

Thermal (heat) capacity is the heat needed to raise the temperature of the whole body by $1^\circ$C, $C=mc$. Specific heat capacity is for unit mass.

(c) Phyllotaxy

Phyllotaxy is the arrangement of leaves on the stem or axis (alternate, opposite, whorled). Anthotaxy is the arrangement of flowers and aestivation is the arrangement of floral parts in the bud.

(a) Virus

COVID-19 is caused by the SARS-CoV-2 coronavirus. Pneumonia is only a possible complication.

(d) 50000 Hz (nearest listed option)

Using $v=f\lambda$:

$f=\frac{v}{\lambda}=\frac{350}{7\times10^{-2}}=5000\ \text{Hz}$

The exact value is 5000 Hz, and the printed options appear to contain a misprint of it, so the 50000 Hz option is the intended one.

(a) Gymnosperms

Gymnosperms (e.g. pine, cycas) bear naked seeds that are not enclosed in a fruit. Angiosperms have seeds enclosed in fruits.

(b) 11.2 km/s

$v_e=\sqrt{2gR}=\sqrt{2\times9.8\times6.4\times10^{6}}\approx1.12\times10^{4}\ \text{m/s}=11.2\ \text{km/s}$

(d) None of above

A chemical change forms new substances, is mostly irreversible and is generally permanent, so (a), (b) and (c) are all wrong.

(a) Crepuscular

Crepuscular animals are active at dawn and dusk. Diurnal animals are active by day and nocturnal animals by night.

(d) Separating funnel

Immiscible liquids form separate layers, and the denser layer is run off through the tap of a separating funnel.

(c) $400\,\mathrm{cm^3}$

The volume displaced equals the volume of the brick:

$V=\frac{m}{\rho}=\frac{1000\ \text{g}}{2.5\ \text{g cm}^{-3}}=400\ \text{cm}^3$

(d) both (a) and (c)

Water is a polar solvent because of the polarity of the O-H bonds, and it dissolves many substances, so it is called the universal solvent.

(c) Increases

The earth is flattened at the poles, so the polar radius is smaller than the equatorial radius. Also $g'=g-R\omega^2\cos^2\lambda$, so $g$ is least at the equator and greatest at the poles.

(a) $\mathrm{m^3\,kg^{-1}\,s^{-2}}$

From $F=\dfrac{Gm_1m_2}{r^2}$:

$G=\frac{Fr^2}{m_1m_2}=\frac{\mathrm{kg\,m\,s^{-2}\cdot m^2}}{\mathrm{kg^2}}=\mathrm{m^3\,kg^{-1}\,s^{-2}}$

(d) H₂CO₃

Carbonic acid is classed as an inorganic compound, like carbonates and CO₂. CHCl₃, CCl₄ and CH₃COOH are organic.