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Q51. Hollandite is an ore mineral of which one of the following elements?
The correct answer is Mn. Hollandite is an oxide mineral primarily known as a significant ore of manganese (Mn) containing barium. Fe (iron) ores include hematite or magnetite. Pt (platinum) is typically found as a native element or in sperrylite. Cr (chromium) is mostly mined from chromite, making the other options incorrect.
Q52. On the magnetic polarity time scale, the present day epoch/chron is called __________.
The correct answer is Bruhnes. Earth's magnetic north and south poles occasionally flip. The current period of 'normal' magnetism, which started about 780,000 years ago, is officially named the Brunhes chron. The Matuyama, Gauss, and Gilbert chrons represent earlier alternating periods of reversed or normal magnetic polarity in Earth's history, meaning they are old and not the present-day epoch.
Q53. Spiti Shale was deposited during the _______ time.
The correct answer is Mesozoic. The Spiti Shale is a famous geological rock formation found in the Himalayas of India, known for rich ammonite fossils. These sediments were laid down primarily during the Jurassic period, which falls squarely in the middle of the Mesozoic Era (the age of dinosaurs). The other eras represent time periods that are either much too old (Proterozoic, Palaeozoic) or too young (Cenozoic), making them incorrect.
Q54. The number of hinge(s) in a monocline is _______.
The correct answer is 2. A hinge in a fold is the point where the rock layer actually bends. A 'monocline' is a step-like fold in otherwise flat rock layers. Because it has to bend down to start the step, and then bend back to become flat again at the bottom, it possesses exactly two hinge points. Thus, 0, 1, and 3 are geologically incorrect.
Q55. The transition from spinel to perovskite structure occurs between _________.
The correct answer is upper mantle and lower mantle. Deep inside the Earth, high pressure causes minerals to change their crystal structure to become denser. The boundary between the upper mantle and lower mantle is defined by the mineral ringwoodite (a spinel structure) transforming into the denser bridgmanite (a perovskite structure). The crust-mantle boundary involves different minerals entirely. The core boundaries involve phase changes of liquid or solid iron, not these silicate crystal structures, making the other options incorrect.
Q56. Which one among the following mineral pairs crystallise early during the cooling of a basaltic melt?
The correct answer is Enstatite and bytownite. As hot magma cools, high-temperature minerals form first. Enstatite is a high-temperature pyroxene, and bytownite is a high-temperature, calcium-rich feldspar. Therefore, they form early on as a pair. Quartz, biotite, and albite (sodium-rich feldspar) form at much lower temperatures at the end of the cooling process, making the other options incorrect pairings.
Q57. Which one of the following causes sediment movement parallel to shoreline in the coastal area?
The correct answer is Longshore current. When ocean waves hit the beach at an angle, they create a current of water that flows parallel along the coastline, dragging sand with it. Rip currents flow directly away from the shore. Backwash is water pulling straight back into the ocean after a wave breaks. Edge waves travel along the coast but are a wave phenomenon, not the primary current that moves sediment. Thus, they are incorrect.
Q58. Which one of the following dams resists external forces by its own weight?
The correct answer is Gravity dam. A gravity dam is a massive structure made of concrete or stone designed to hold back water entirely by using its own heavy weight. An earthen dam uses compacted soil but relies on slopes rather than sheer vertical weight. 'Storage' and 'Detention' describe a dam's purpose (what it does with the water), not its structural engineering mechanism, so they are incorrect.
Q59. Which one of the following dinosaur fossils is a theropod?
The correct answer is Rajasaurus. Theropods were a group of bipedal (walking on two legs), mostly carnivorous dinosaurs. Rajasaurus is a famous carnivorous theropod discovered in India. Kotasaurus, Titanosaurus, and Barapasaurus were all massive, four-legged, plant-eating dinosaurs known as sauropods, making them incorrect choices.
Q60. Which one of the following gastropod genera displays sinistral coiling?
The correct answer is Physa. Most snail shells coil to the right. However, 'sinistral' coiling means the shell coils to the left. The genus Physa is famous because it is a freshwater snail that naturally coils to the left. Cypraea (cowries), Murex, and Conus are all sea snails that typically coil to the right (dextral), making them incorrect.