Your Answer : (Not Answered)

Correct Answer : D

The correct match is (iv) - (q): nitrogen in NO₂ has oxidation state +4.

Taking oxygen as -2, the oxidation state of nitrogen in each compound is:

• N₂: 0, as in any element.
• NO: \(x - 2 = 0\), so +2.
• N₂O: \(2x - 2 = 0\), so +1.
• NO₂: \(x - 4 = 0\), so +4.

So the full matching is (i)-(r), (ii)-(s), (iii)-(p), (iv)-(q). The options (i)-(s), (ii)-(p) and (iii)-(r) each give a compound the value that belongs to another one.

Your Answer : (Not Answered)

Correct Answer : D

The pyramid of energy is always upright.

Each trophic level passes on only about 10% of the energy it receives to the next, the rest being lost as heat in respiration. Energy flow at each higher level must therefore be smaller than at the level below, in any ecosystem.

Pyramids of number or biomass can be inverted: a forest has few large trees supporting many insects, so its pyramid of numbers is spindle shaped or inverted. But energy cannot increase up the chain, so the energy pyramid is never inverted, spindle shaped or dumb-bell shaped.

Your Answer : (Not Answered)

Correct Answer : B

The pea experiments were done by Gregor Johann Mendel.

Mendel, an Austrian monk, crossed pea plants in his monastery garden in the 1850s and 1860s. He studied traits that come in contrasting pairs, such as tall or short, round or wrinkled seeds, yellow or green seeds, and found the laws by which they are inherited. He is called the father of genetics.

Dr. M.S. Swaminathan is the Indian agricultural scientist associated with the Green Revolution. George de Mestral, a Swiss engineer, invented Velcro after noticing burrs sticking to his dog. Charles Darwin proposed the theory of evolution by natural selection.

Your Answer : (Not Answered)

Correct Answer : B

Only citrus canker (printed 'tanker') is bacterial, so the answer is Only (b).

Citrus canker is caused by the bacterium Xanthomonas, which produces raised corky lesions on leaves, twigs and fruit.

Rust of wheat is caused by fungi of the genus Puccinia, and yellow vein mosaic of bhindi (okra) is caused by a virus spread by whiteflies. Options including a or c are therefore wrong.

Your Answer : (Not Answered)

Correct Answer : A

The set of communicable diseases is tuberculosis, cholera, measles.

Communicable diseases are caused by microbes and spread from person to person: tuberculosis (a bacterium, through the air), cholera (a bacterium, through contaminated water and food) and measles (a virus, through the air).

Each other set includes a non-communicable disease: hypertension, asthma and cancer do not spread from one person to another. Common cold, common flu and chickenpox are communicable, but a set containing even one non-communicable disease is not a set of communicable diseases.

Your Answer : (Not Answered)

Correct Answer : B

The disease is malaria.

Malaria, spread by the female Anopheles mosquito, causes high fever with shivering and chills. Quinine, obtained from the bark of the Cinchona tree, was for centuries the main medicine against it.

Typhoid is a bacterial infection spread through contaminated food and water, and dengue and chikungunya are viral fevers spread by Aedes mosquitoes. None is treated with cinchona bark.

Your Answer : (Not Answered)

Correct Answer : A

The correct matching is (a)-(iv), (b)-(i), (c)-(ii), (d)-(iii).

Adrenal hormones regulate the body's salt and water balance, so their deficiency causes salt imbalance (a-iv). Too little growth hormone in childhood causes dwarfism (b-i). Thyroxine needs iodine, and its deficiency causes goitre, a swollen thyroid (c-ii). Too little insulin causes diabetes, because blood sugar is not controlled (d-iii).

The other options swap these, for example linking thyroxine with diabetes or insulin with goitre.

Your Answer : (Not Answered)

Correct Answer : C

The mismatched pair is Adrenaline - Pituitary Gland.

Adrenaline is secreted by the adrenal glands, which sit on top of the kidneys. It prepares the body for emergencies by raising heart rate, blood pressure and blood sugar.

The other pairs are correct: estrogen is made by the ovaries, thyroxine by the thyroid gland, and testosterone by the testes. The pituitary gland makes hormones such as growth hormone and the hormones that control other glands, but not adrenaline.

Your Answer : (Not Answered)

Correct Answer : C

Metamorphosis in frogs is controlled by Thyroxine.

Thyroxine, the hormone of the thyroid gland, triggers the change from tadpole to adult frog. If the water lacks iodine, which the thyroid needs to make thyroxine, tadpoles fail to change into adults; in experiments, adding thyroxine speeds up the change.

Adrenaline prepares the body for emergencies. Growth hormone from the pituitary controls growth in size. Insulin from the pancreas controls blood sugar. None of them drives metamorphosis.

Your Answer : (Not Answered)

Correct Answer : C

The true statements are (A), (C) and (D).

Whales and dolphins are mammals: they breathe air through nostrils, the blowholes on top of the head, and must come to the surface regularly to breathe. They cannot use the oxygen dissolved in water.

They have lungs, not gills, so (B) is false, and every option containing (B) is wrong.

This is why whales and dolphins can drown if they are trapped underwater, unlike fish, which take oxygen from the water through their gills.

Your Answer : (Not Answered)

Correct Answer : D

(A), (B), (C) are Thyroxine, Thyroid, Iodine.

Thyroxine, secreted by the thyroid gland, regulates the metabolism of carbohydrates, proteins and fats. The thyroid needs iodine to make thyroxine, so a diet lacking iodine leads to goitre, a swelling of the gland.

Growth hormone mainly controls growth, insulin regulates blood sugar, and adrenaline prepares the body for emergencies; none matches all three blanks.

Your Answer : (Not Answered)

Correct Answer : C

Statements (a), (b) and (d) are true.

Rainwater harvesting collects rainwater from roofs and land and stores it or directs it into the ground. It recharges and so conserves groundwater (a), reduces surface run-off and hence local flooding (b), and the stored water can be used for purposes such as irrigating crops (d).

It does not create drainage problems; by reducing run-off it eases the load on drains, so (c) is false and every option including it is wrong.

Your Answer : (Not Answered)

Correct Answer : D

The practice not likely to increase soil fertility is maintaining minimum distance between the crops while sowing.

Sowing seeds too close together does not add anything to the soil. It causes overcrowding, so plants compete for the same nutrients, water and sunlight, and the soil is drained faster rather than enriched.

The other practices all help restore fertility. Organic manure adds humus and nutrients and improves soil texture. Leaving a field fallow between crops lets the soil recover its nutrients. Crop rotation, especially with legumes, replenishes nitrogen.

Your Answer : (Not Answered)

Correct Answer : B

The correct matching is a-v, b-iv, c-i, d-ii, e-iii.

Biodegradable materials made from plants and animals decompose at very different rates. Kitchen waste such as a banana peel breaks down in a week or two, paper in a few weeks (about 10-30 days), a cotton shirt in a few months (2-5 months) and a silk scarf, made of animal protein fibre, is usually given as about 4 years. A plastic bottle is not biodegradable in any useful sense and lasts for many years.

The answer can be fixed from the two clearest pairs alone: plastic lasts several years (a-v) and cotton cloth decays in a few months (c-i). Only option 2 has both; options 1 and 3 give plastic only 4 years, and option 4 gives cotton 1-2 weeks.

Your Answer : (Not Answered)

Correct Answer : A

Both (A) and (R) are true but (R) is not the correct explanation of (A).

The assertion is true: the nucleus is a distinct, usually spherical structure, typically near the centre of the cell. The reason is also true: the nucleus lies in the cytoplasm, the jelly-like substance between it and the cell membrane.

But being surrounded by cytoplasm is not why the structure is called the nucleus or why it is spherical and central. The two statements are separate facts, so (R) does not explain (A).

Your Answer : (Not Answered)

Correct Answer : D

The set in which all show external fertilisation is Frogs, fish, starfish.

In external fertilisation eggs and sperm are released into water and fuse outside the body. Frogs and most fish release eggs and sperm in water, and starfish shed their gametes into the sea.

Hens, lizards and butterflies all have internal fertilisation, so any set containing one of them fails.

Your Answer : (Not Answered)

Correct Answer : B

The words in order are zygote, embryo, uterus, foetus.

Fertilisation of the egg by the sperm forms a single cell, the zygote (W), which divides repeatedly into a ball of cells. As the cells begin to form tissues and organs, the developing structure is called the embryo (X), and it becomes embedded in the wall of the uterus (Y). Once all the body parts can be identified, the embryo is called a foetus (Z).

Option 1 swaps embryo and foetus. Options naming the fallopian tube are wrong because fertilisation happens there, but implantation takes place in the uterus, and option 3 also puts embryo before zygote.

Your Answer : (Not Answered)

Correct Answer : A

The animal is the snake.

A snake has a long backbone made of many vertebrae, with many muscles attached to it. By contracting these muscles it bends its body into loops, and each loop pushes against the ground, moving the snake forward. This description follows the NCERT chapter on body movements.

The earthworm and hook worm have no backbone at all; the earthworm moves by alternately contracting and extending its body with the help of tiny bristles. The snail moves with a muscular foot and has a shell, not a backbone.

Your Answer : (Not Answered)

Correct Answer : C

Gills absorb dissolved oxygen from water.

Fish take in water through the mouth and pass it over the gills. The gills have thin filaments richly supplied with blood vessels, through which oxygen dissolved in the water diffuses into the blood and carbon dioxide diffuses out.

Fish do not take in oxygen from air; that is the role of lungs in land animals. Nutrients are absorbed in the intestine, not the gills. Although some wastes such as ammonia do pass out through the gills, their main function is gaseous exchange.

Your Answer : (Not Answered)

Correct Answer : A

Both S1 and S2 are true.

Photosynthesis is endothermic: plants absorb light energy to make glucose from carbon dioxide and water, storing that energy in chemical bonds.

Respiration is exothermic: glucose is oxidised to carbon dioxide and water, releasing energy that the cell captures as ATP and partly loses as heat. The two processes are energetically opposite, so the options declaring either one false are wrong.