General Science Previous Year Questions (PYQ) with Answers – Page 38

The inner lining of the mouth and the oesophagus is made of squamous epithelium, so an injury to that lining damages this tissue.

Both are stored forms of glucose, but plants store it as starch and animals as glycogen. Starch and glycogen are polysaccharides, long chains of glucose units.

Genetic modification is used in plants, animals and microbes alike, so this statement is false. A genetically modified organism is one whose DNA has been changed, usually by taking a useful gene from one organism and putting it into another.

The chloride ion has 18 electrons, while the magnesium ion has only 10, so the two are not isoelectronic. Isoelectronic species have the same number of electrons.

The trapped steam raises the pressure inside the cooker, and at higher pressure water boils at a higher temperature, so food cooks faster.

Two ammonium ions, each with a charge of +1, are needed to balance one carbonate ion with a charge of -2.

Putting a soft iron bar inside a solenoid makes the magnetic field much stronger, so the claim that the field stays the same is not correct.

Metals produce a ringing sound when struck, a property called sonority, which is why bells are made of metal. Sonorous means 'producing a deep, ringing sound'.

Cyclohexane, C 6 H 12, has 6 C–C single bonds and 12 C–H single bonds, 18 single bonds in all and no double or triple bond.

Silver and copper are the two best conductors of heat among metals. Metals conduct heat because their free electrons carry energy quickly through the solid.

Bacteria turn the lactose in milk into lactic acid, a new substance, so souring is a chemical change that cannot be reversed.

One kilowatt-hour is the energy used by a 1 kW appliance running for one hour: 1000 W × 3600 s = 3.6 × 10⁶ J. The joule is too small for household bills, so electricity companies charge in kilowatt-hours, commonly called units.

Crude petroleum is a mixture of hydrocarbons with different boiling points, and fractional distillation separates them. In a refinery, crude oil is heated to about 400 °C and its vapour enters a tall fractionating column that is hot at the bottom and cooler towards the top.

Unsaturated hydrocarbons have a high carbon content and burn with a yellow, sooty flame, while saturated ones usually burn with a clean blue flame.

Milk of magnesia is a suspension of magnesium hydroxide, a mild base that neutralises excess stomach acid without harming the body.

Methanoic acid, better known as formic acid, is the acid that ants inject when they sting, which is why the bite burns.

The stinging hairs of the nettle inject methanoic acid, also called formic acid, which causes the burning pain. Nettle is a herbaceous plant whose leaves carry fine, brittle hairs.

Field lines always leave a conductor normal to its surface, and for a positive charge they point away from it.

Each piece has a resistance of 10 ohm, and five equal 10-ohm resistors in parallel give 10 ÷ 5 = 2 ohm.

This is a double displacement (precipitation) reaction, in which no element gains oxygen or loses electrons. When the two solutions are mixed, the ions swap partners: BaCl2 + Na2SO4 → BaSO4 + 2NaCl.