Identify the cloud on the basis of the following characteristics relating to it : I. They look like cotton wool. II. They exist in patches and have flat base. III. They are generally formed at a height of 4 to 7 km. Select the answer using the code given below :

The correct answer is D, Bauxite. Bauxite is a mixture of hydrated aluminium oxides and hydroxides, not a silicate, and it is the main ore of aluminium.

Silicates are minerals built from silicon-oxygen tetrahedra, and they make up most of the earth's crust. Bauxite forms when rocks rich in aluminium are deeply weathered in hot, wet tropical climates, which washes the silica away and leaves aluminium oxide behind; minerals such as gibbsite and boehmite give it its value. In India it is mined mainly in Odisha, along with Gujarat, Jharkhand and Chhattisgarh.

Option A is wrong because feldspar, an aluminosilicate of potassium, sodium or calcium, is the most common mineral group in the crust and is used in ceramics and glass. Option B is wrong because zeolites are porous hydrated aluminosilicates used as water softeners and catalysts. Option C is wrong because mica is a sheet silicate that splits into thin layers and is valued as an electrical insulator; Jharkhand, Andhra Pradesh and Rajasthan are known for it.

Exam tip: feldspar, mica, zeolite = silicates; bauxite = aluminium oxide ore, Odisha leads.

The correct answer is A, 1 only. Only the Aral Sea has shrunk drastically because of human activity.

The Aral Sea, on the border of Kazakhstan and Uzbekistan, was once the world's fourth-largest lake. From the 1960s, Soviet planners diverted its two feeder rivers, the Amu Darya and the Syr Darya, to irrigate cotton fields, and the lake lost most of its area, splitting into smaller bodies and leaving a salty desert, the Aralkum. The Black Sea is a large inland sea joined to the Mediterranean through the Bosporus and has not dried up. Lake Baikal in Siberia, the world's deepest and oldest freshwater lake, faces pollution but has not shrunk away.

B is wrong: neither the Black Sea nor Lake Baikal has dried up.

C is wrong: the Black Sea has not shrunk.

D is wrong: Lake Baikal has not shrunk immensely.

Exam tip: Aral Sea = Amu Darya and Syr Darya diverted for cotton; Baikal = deepest lake in the world.

The correct answer is B, Congo Basin. The Cuvette Centrale peatland of the Congo Basin is the world's largest tropical peatland.

Scientists mapped this vast peat swamp only in 2017, spread across the Republic of the Congo and the Democratic Republic of the Congo. It covers about 1.45 lakh square kilometres and stores roughly 29 billion tonnes of carbon, about three years of the world's fossil-fuel emissions. Peat forms when waterlogged plant matter does not fully decay, so draining it for farming, logging or oil drilling would release this carbon and worsen climate change.

A is wrong: the Amazon has peatlands too, but the largest single tropical peatland is in the Congo Basin.

C is wrong: the Kikori Basin in Papua New Guinea is a much smaller rainforest river basin.

D is wrong: the Rio de la Plata Basin in South America is mostly grassland, wetland and farmland, not the largest peatland.

Exam tip: Cuvette Centrale, Congo Basin = largest tropical peatland, about 29 billion tonnes of carbon.

The correct answer is A, the savanna of Kenya and Tanzania. The Masai are a cattle-keeping people of the East African savanna, moving their herds with the seasonal rains; their life is the standard textbook example of pastoral nomadism in the tropical grasslands. B is wrong because the people of the Congo rainforest named in textbooks are the Pygmies or Bambuti, who live by hunting and gathering. C is wrong because the Kalahari is the home of the Bushmen or San, also hunters and gatherers, who are famous for tracking and for finding water in a dry land. D is wrong because the steppes of Ukraine are a wheat growing belt of commercial farming, not the home of a named pastoral tribe in the exam syllabus. Match each people with its biome.

The correct answer is C, the Urals. The Ural mountains, an old worn range running north to south across Russia, together with the Ural river, the Caspian Sea and the Caucasus, form the conventional boundary between Europe and Asia, which is why the two are often treated as one land mass called Eurasia. A is wrong because the Alps are young fold mountains within Europe, dividing Italy from France, Switzerland and Austria, and holding Mont Blanc. B is wrong because the Pyrenees separate France from Spain and shelter the small state of Andorra. D is wrong because the Apennines run the length of the Italian peninsula. Only the Urals serve as a continental boundary, and they are also rich in iron, coal and other minerals.