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Q61. For a soil, Liquidity Index = (Natural Water Content - X) / Plasticity Index. Here, X is:
Liquidity Index (LI) compares natural water content to the Atterberg limits. The formula is (w - Plastic Limit) / (Liquid Limit - Plastic Limit).
Q62. Which sandstone is well-sorted, contains up to 75% quartz, and has rock fragments in excess of feldspar?
Lithic arenite is defined by having significant rock fragments (lithics) > feldspars. Arkose is feldspar-rich. Quartz arenite is >95% quartz.
Q63. During which of the following geological eras did birds and mammals first appear on the Earth?
Mammals appeared in the Triassic and Birds in the Jurassic; both periods belong to the Mesozoic Era. The Cenozoic is the 'Age of Mammals' but not their origin.
Q64. Mid-Oceanic ridges mark _______ plate margins and can be traced by belts of _____ focus earthquakes.
Mid-Oceanic ridges are divergent (constructive) boundaries where new crust forms. Earthquakes here are shallow because the lithosphere is thin and hot. Destructive margins (subduction) host deep quakes.
Q65. A type of unconformity characterized by the occurrence of sedimentary rocks on igneous/metamorphic rocks is known as:
Nonconformity occurs when sedimentary rock rests on top of older eroded igneous or metamorphic rock.
Q66. Which one of the following is the optical spectral window suitable for remote sensing?
Optical remote sensing generally covers the Visible (0.4-0.7), Near IR, SWIR, and Thermal IR regions. The range 0.4 – 14 µm encompasses these useful optical windows.
Q67. The correct chronological order (older to younger) of these volcanic events: (P) Rajmahal, (Q) Deccan, (R) Panjal, (S) Malani.
Order: Malani (Precambrian) -> Panjal (Carboniferous-Permian) -> Rajmahal (Early Cretaceous) -> Deccan (Late Cretaceous).
Q68. Which one of the following stable isotopic ratios is used for estimation of palaeo-temperature of seawater?
Oxygen isotope fractionation (d18O) in foraminifera shells is the standard proxy for reconstructing past ocean temperatures.
Q69. Which mineral assemblage is stable in a pelitic rock in the greenschist facies?
Pelitic rocks (Al-rich) in greenschist facies typically contain muscovite, chlorite, biotite, and quartz. Albite/actinolite is for mafic rocks.
Q70. Identify the microscope component using: Pleochroism of biotite.
Pleochroism is observed in Plane Polarized Light (Analyzer removed). Rotating the stage changes absorption relative to the Polarizer direction.