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Q151. Which one of the following defines a hexagonal dipyramid?
The correct answer is A mirror plane that is perpendicular to the vertical six fold axis of symmetry. A 'dipyramid' looks exactly like two standard pyramids glued together at their flat bases. Mathematically, for the top pyramid to perfectly mirror the bottom pyramid and create this closed 3D shape, there absolutely MUST be a flat, horizontal mirror plane cutting right through the middle, perfectly perpendicular to the main vertical rotation axis.
Q152. An ore mineral has the following physical properties: (1) metallic lustre, (2) steel-grey color, (3) two sets of octahedral cleavage, (4) high specific gravity, and (5) makes mark on paper. Identify the ore mineral.
The correct answer is galena. Galena is the primary ore of lead. It is notoriously heavy (high specific gravity), boasts a shiny steel-grey metallic lustre, and is soft enough to easily leave a grey mark on a piece of paper. Magnetite is hard and black. Bornite is known for its purple-blue tarnish ('peacock ore'). Sphalerite is usually brown/yellow with a resinous lustre. (Note: Galena is renowned for cubic cleavage, though the question's phrasing regarding cleavage may be imperfect, its other traits strictly define galena).
Q153. Dicroidium is known from the
The correct answer is Panchet Formation. Dicroidium is a famous extinct genus of seed ferns that dominated the Triassic period in Gondwana. In Indian stratigraphy, the Panchet Formation is a classic Lower Triassic rock sequence where these Dicroidium fossils are prominently found. The Raniganj Formation is older (Permian) and characterized by Glossopteris. The Pachmarhi and Denwa are later Triassic formations.
Q154. Fossils of burrows and footprints are known as
The correct answer is trace fossils. Fossils that preserve the activity or behavior of an organism, rather than its physical remains, are termed 'trace fossils' (or ichnofossils). Burrows and footprints fit this definition perfectly. 'Pseudofossils' are natural rocks that just look like fossils. 'Coprolites' specifically refer to fossilized feces. 'Body fossils' are the actual preserved bones, shells, or body parts of the organism.
Q155. Horst and graben structures are typically formed by
The correct answer is normal faulting. When the Earth's crust is pulled apart (extensional stress), it cracks into blocks. The blocks that slide down form valleys called 'grabens', and the blocks left standing high form ridges called 'horsts'. This up-and-down block movement is strictly caused by 'normal faulting'. Reverse and thrust faulting happen when rocks are compressed together, and strike-slip faulting involves horizontal side-to-side motion.
Q156. Match the bivalves in Group I with their modes of life in Group II
The correct answer is Gryphaea - Unattached, free-lying, Mya - Burrowing, Mytilus - Sessile byssate, Pecten - Swimming. Gryphaea ('Devil's toenail') rested freely on the muddy sea floor. Mya clams are infaunal, digging deep burrows into the sand. Mytilus mussels use strong byssal threads to attach themselves firmly to rocks (sessile byssate). Pecten (scallops) are famous for rapidly clapping their shells to swim away from predators.
Q157. Match the features in Group I with their characteristic rocks / rock suite in Group II.
The correct answer is Continental arc - Andesite, Mid-oceanic ridge - Olivine tholeiite, Collision zones - Ophiolite, Continental rift - Alkaline rock. Continental arcs famously erupt intermediate magmas like Andesite. Mid-ocean ridges erupt enormous volumes of basalt, specifically Olivine tholeiite. When continents collide, slices of the ocean floor get wedged up into the mountains, forming Ophiolites. Continental rifts often feature unique, deep-sourced magmas resulting in Alkaline rocks.
Q158. Match the fuels in Group I with corresponding areas of occurrence in Group II.
The correct answer is Uranium - Jaduguda, Lignite - Vastan, Bituminous Coal - Singrauli, Petroleum - Digboi. Jaduguda in Jharkhand is India's most famous and first uranium mine. Vastan in Gujarat is renowned for its thick lignite (brown coal) seams. Singrauli in Madhya Pradesh is a massive hub for high-grade bituminous coal mining. Digboi in Assam holds the historical distinction of being the oldest operational petroleum oil well in India.
Q159. Match the geomorphic features in Group I with corresponding environments in Group II.
The correct answer is Eskers - Glacial, Natural levee - Fluvial, Chenier ridge - Beach, Plug dome - Volcanic. Eskers are winding ridges of gravel deposited by meltwater streams under glaciers. Natural levees are built by rivers (fluvial) overflowing their banks. Chenier ridges are sandy deposits found along muddy beach coastlines. Plug domes are steep-sided mounds formed by thick volcanic lava.
Q160. Match the metal deposits in Group I with the corresponding processes in Group II.
The correct answer is Aluminum - Residual concentration, Iron - Chemical sedimentation, Tungsten - Contact metasomatism, Thorium - Mechanical concentration. Aluminum (Bauxite) forms when extreme tropical weathering washes everything away, leaving a 'residual' crust of aluminum behind. Massive Iron deposits (BIFs) precipitated directly from ancient oceans (Chemical sedimentation). Tungsten (Scheelite) forms when hot magma bakes adjacent limestone (Contact metasomatism). Thorium (Monazite) is heavy and gets concentrated into placer sands by rivers and waves (Mechanical concentration).