Which one from among the following planets is largest in size?

The correct answer is A, Lonar Lake. Lonar Lake in Buldhana district of Maharashtra fills a crater made by a meteorite impact.

The Lonar crater was formed in prehistoric times when a meteorite struck the basalt rock of the Deccan Plateau. It is about 1.8 km across, and the lake inside it is both saline and alkaline. It is one of the very few known hypervelocity impact craters in basaltic rock anywhere on Earth, which makes it important to geologists. It has been declared a Ramsar site and is a geo-heritage site.

B is wrong: Sambhar in Rajasthan is India's largest inland salt lake, formed in a shallow basin, not a crater.

C is wrong: Chilika in Odisha is a brackish-water lagoon on the east coast, Asia's largest.

D is wrong: Vembanad in Kerala is a long backwater lagoon fed by several rivers.

Exam tip: Lonar = meteorite crater lake (Maharashtra); Sambhar = salt lake; Chilika = lagoon; Wular = largest freshwater lake.

The correct answer is C, Polynesia. New Zealand forms the south-western corner of the Polynesian Triangle in the Pacific Ocean.

The Pacific islands are grouped into three regions. Polynesia ("many islands") is a vast triangle with Hawaii in the north, Easter Island in the east and New Zealand in the south-west; it also includes Samoa, Tonga and Tahiti. The Maori, New Zealand's first people, are Polynesians who reached the islands by canoe around the 13th century, and their language is close to Hawaiian and Tahitian.

A is wrong: Micronesia ("small islands") lies north of the equator and includes Guam, the Marshall Islands and Kiribati.

B is wrong: Melanesia covers Papua New Guinea, Fiji, the Solomon Islands, Vanuatu and New Caledonia, north-west of New Zealand.

D is wrong: the Hawaiian chain is a single archipelago at the northern tip of Polynesia, far from New Zealand.

Exam tip: Polynesian Triangle corners = Hawaii, Easter Island, New Zealand; Fiji is Melanesia; Guam is Micronesia.

The correct answer is B, Desert, Tropical thorny, Moist deciduous, Mangrove. The route runs from the dry west to the wet east coast, so the vegetation changes as rainfall rises.

Bikaner lies in the Thar Desert of western Rajasthan, where rainfall is below about 25 cm and only desert plants such as khejri and cactus grow. Moving east through eastern Rajasthan and the drier parts of central India, rainfall of roughly 25 to 70 cm supports tropical thorn forests of acacia, babool and ber. Further east, in Chhattisgarh, Jharkhand and Odisha, rainfall of about 100 to 200 cm supports moist deciduous forests of sal and teak. Konark is on the Odisha coast near the Mahanadi delta, where tidal creeks support mangroves.

A is wrong: it puts thorny vegetation before the desert, but Bikaner itself is in the desert.

C is wrong: it starts with moist deciduous forest and ends with desert, the reverse of the journey.

D is wrong: mangroves grow only at the coast, so they must come last, after the inland deciduous forests.

Exam tip: more rain, richer forest: desert < thorn < dry deciduous < moist deciduous < evergreen; mangroves on tidal coasts.

The correct answer is D, Olivine. Olivine is a silicate of magnesium and iron that forms greenish crystals and is common in basalt.

Olivine takes its name from its olive-green colour. It crystallises early from hot magma that is low in silica, which is why it turns up in basalt, gabbro and peridotite and makes up much of the Earth's upper mantle. Its main elements are magnesium, iron and silica. A clear, gem-quality olivine is sold as the jewel peridot. Feldspar and quartz, by contrast, are the commonest minerals of the crust and are richer in silica.

A is wrong: amphibolite is a metamorphic rock made mostly of amphibole minerals, not a single mineral.

B is wrong: feldspar is made of silicon and oxygen with sodium, potassium, calcium and aluminium, and is light cream to salmon pink.

C is wrong: pyroxene contains calcium and aluminium along with magnesium, iron and silica, and is usually green or black.

Exam tip: olivine = green, Mg-Fe silicate, basalt, gem peridot; feldspar = half of the crust.

The correct answer is C, New Guinea. With an area of about 7.86 lakh sq km, New Guinea is the world's second-largest island, after Greenland.

New Guinea lies just north of Australia and is shared by two countries: its western half belongs to Indonesia and its eastern half is the mainland of Papua New Guinea. It is mountainous and covered with dense rainforest. Australia is not counted here because it is treated as a continent. After Greenland and New Guinea, the next largest islands are Borneo, Madagascar, Baffin Island and Sumatra, in that order.

A is wrong: Borneo, shared by Indonesia, Malaysia and Brunei, is the third largest, at about 7.43 lakh sq km.

B is wrong: Madagascar, off the south-east coast of Africa, is fourth, at about 5.87 lakh sq km.

D is wrong: Sumatra, in Indonesia, is sixth, at about 4.73 lakh sq km.

Exam tip: largest islands in order: Greenland, New Guinea, Borneo, Madagascar, Baffin, Sumatra.