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Q171. Which of the following changes occurred during the evolution of Equidae?
The correct answer is Lengthening of skull in front of the orbit. As horses (Equidae) evolved over millions of years to graze on harsh prairie grasses, their skulls elongated significantly in front of their eyes to accommodate massive, high-crowned teeth. The number of lateral toes drastically decreased (not increased) down to a single hoof. Their teeth increased in hypsodonty (high-crowned), and their limb ratios changed for fast running.
Q172. Which of the following is associated with a divergent plate boundary?
The correct answer is Ridge. A divergent plate boundary occurs where two tectonic plates move away from each other, allowing magma to rise and create new crust, typically forming a mid-ocean 'Ridge'. A 'Trench', 'Island arc', and 'Accretionary prism' are all features strictly associated with convergent plate boundaries where plates crash into one another.
Q173. Which of the following is the fundamental constituent of humic coal?
The correct answer is Maceral. Just as rocks are made of minerals, coal is microscopically composed of different organic plant components called 'macerals'. Thus, macerals are the fundamental microscopic building blocks of humic coal. Mineral matter is the inorganic dirt impurity. Lithotypes are the macroscopic, visible bands in coal (like vitrain or fusain). Kerogen is the waxy precursor to petroleum, not coal.
Q174. Which of the following mineral assemblages characterizes blueschist facies metamorphism of a mafic rock?
The correct answer is Glaucophane + lawsonite. Blueschist facies metamorphism occurs in subduction zones under conditions of high pressure but very low temperature. When a mafic rock (like basalt) experiences this, it forms the blue amphibole 'glaucophane' alongside 'lawsonite'. Hornblende and plagioclase characterize the hotter amphibolite facies. Omphacite and garnet represent the extreme high-pressure eclogite facies. Phengite/chlorite can appear in lower-grade greenschists.
Q175. Which of the following rocks occurs typically in a ductile shear zone?
The correct answer is Mylonite. Deep in the Earth where it is hot, rocks caught in a fault zone behave like plastic and stretch or smear without shattering (ductile shear). This process creates a finely banded, stretched rock called a 'mylonite'. Gouge and breccia form in cold, shallow zones where the rock brutally shatters and grinds (brittle shear). Pseudotachylite forms from extreme friction melting the rock during a sudden earthquake.
Q176. Which of the following statements are correct? I. In a planar tabular cross-bedding, the upper and lower bounding surfaces are planar and parallel. II. In a planar tabular cross-bedding, the upper and lower bounding surfaces are planar but not parallel. III. In a trough cross-bedding, both the upper and the lower bounding surfaces are curved. IV. In a trough cross-bedding, the upper bounding surface is planar and the lower bounding surface is curved.
In 'planar tabular cross-bedding', the overall beds are separated by straight, flat (planar) bounding surfaces that run parallel to each other. In 'trough cross-bedding', the scooped-out lower bounding surfaces are curved. Sometimes the top surface of a trough is truncated flat (planar), or both top and bottom can be curved depending on the erosion. Only statement II is completely incorrect.
Q177. Among the following, the mineral showing acicular habit is
The correct answer is sillimanite. 'Habit' describes the physical shape a crystal prefers to grow in. An 'acicular' habit means the mineral grows as long, incredibly thin, needle-like crystals. Sillimanite is famous for growing in these fibrous, needle-like shapes. Kyanite usually grows as bladed crystals, biotite as flat sheets, and tourmaline as chunky prisms.
Q178. Fissility is best shown by
The correct answer is shale. 'Fissility' is a rock's ability to easily split into incredibly thin, flat sheets. Shale is made of microscopic, flat clay particles that get pressed perfectly parallel to each other, allowing it to split like pages in a book. Sandstone and limestone break into chunky blocks, not paper-thin sheets.
Q179. In which one of the following tectonic settings are the highest mountain chains and thickest crust found?
The correct answer is Continental collision. Earth's crust gets its absolute thickest when two massive, buoyant continental plates crash directly into each other. Because neither plate wants to sink deep into the mantle, they buckle and stack upwards like a car crash, pushing up to form the highest mountain chains on Earth, like the Himalayas.
Q180. Petroleum is NOT commercially produced from
The correct answer is Vindhyan basin. Petroleum (oil and gas) forms from dead organic matter trapped in sedimentary rocks. The Krishna-Godavari, Cauvery-Palar, and Cambay basins are all famous, active oil-producing regions in India. The Vindhyan basin is extremely ancient (Precambrian) and mostly contains barren rocks without commercial petroleum reserves.