General Science Previous Year Questions (PYQ) with Answers – Page 66

Paper chromatography separates substances because each one divides, or partitions, itself differently between two liquid phases. In paper chromatography the stationary phase is the water held in the cellulose fibres of the paper, and the mobile phase is the solvent that rises up the paper by capillary action.

Sound in air is a longitudinal wave, and only transverse waves can be polarised. Polarisation means restricting the vibrations of a wave to a single plane.

The Moon gives out no light of its own; it only reflects sunlight, so it is a non-luminous object. A luminous object produces and emits its own light, while a non-luminous object is seen only because it reflects light falling on it.

The heat needed is 50 cal to warm the ice to 0°C, 800 cal to melt it, and 200 cal to warm all 20 g of water to 10°C. Take the specific heat of ice as 0.5 cal/g°C, the latent heat of fusion of ice as 80 cal/g and the…

For a real object, a concave lens always forms a virtual image, so this statement is wrong. A concave lens is a diverging lens: it spreads out parallel rays so that they seem to come from its focus on the same side as the object.

With no work done, the first law of thermodynamics reduces to ΔU = Q, so the change in internal energy equals the heat that flows in or out.

Quartz is silicon dioxide (SiO 2 ), so it contains silicon and oxygen. Quartz is one of the most common minerals in the Earth's crust and the main part of sand.

Root hairs are thin outgrowths of the root's epidermal cells that greatly increase the area for absorbing water and minerals.

A shoot growing towards the light is moving in the direction of the stimulus, which makes it a positive tropism.

Both are cnidarians, simple aquatic animals with stinging cells. Members of phylum Coelenterata (Cnidaria) have radial symmetry, two body layers, a single opening that works as both mouth and anus, and stinging cells called cnidoblasts on their tentacles, used to catch prey and for defence.

The Himalayan nettle yields a strong natural fibre that can be spun and woven into cloth. Girardinia diversifolia, known as Himalayan giant nettle or allo, is a stinging shrub that grows wild in the moist forests of the Himalayas, including Uttarakhand, Himachal Pradesh and the North-east, as well as Nepal.

The statement is Kirchhoff's voltage (loop) law, and it follows from the fact that energy is neither created nor destroyed.

Phreatophytes are deep-rooted plants that survive in dry regions by drawing water from the water table. The name comes from the Greek for 'well plant'.

Average velocity is total displacement divided by time, and the car ends where it started, so its displacement is zero.

Chlorine released from chlorofluorocarbons destroys ozone fastest where polar stratospheric clouds form in the extreme cold of winter, because those ice clouds hold the chlorine compounds that sunlight then breaks up; the thinning is therefore deepest over Antarctica, where it is called the ozone hole, and is seen over the…

A metal more reactive than hydrogen displaces it from a dilute acid, so zinc with dilute sulphuric acid gives zinc sulphate and hydrogen gas, and this is the standard laboratory preparation of the gas; the test is that it burns with a pop.

Each statement is true: there are plant-eating turtles, fish and marine mammals, and some snakes give birth to live young.

Both have 10 electrons, the same number as a neon atom, so they are isoelectronic. Isoelectronic species have the same number of electrons.

About an axis through the centre, a solid disc has I = ½MR² while a solid sphere has I = ⅖MR², and ½ is larger than ⅖.

Magnesium does not react with cold water; it reacts with hot water and burns in steam to form magnesium oxide and hydrogen.