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Q151. Which one of the given gases in the atmosphere is the most important for chemical weathering on the surface of the Earth?
Carbon dioxide dissolves in rainwater to form carbonic acid (H2CO3), which is the primary natural acid responsible for the chemical weathering (carbonation) of silicate and carbonate rocks.
Q152. The amount of dissolved Na+ in seawater is constant over time, whereas that of Ca2+ dissolved is not. This is because:
Calcium (Ca2+) is heavily extracted from seawater by a vast number of marine organisms to build calcareous shells and skeletons, making its concentration highly variable. Sodium (Na+) lacks this massive biological sink.
Q153. In the southern hemisphere, Earth's magnetic field and its horizontal component respectively are:
By convention, downward points positive. In the Southern Hemisphere, magnetic field lines point upward and out of the Earth (negative Z). The horizontal component (H) always points toward magnetic north and is always positive.
Q154. Which one of the following molecules is the most buoyant in the atmosphere?
Buoyancy depends on molar mass. Dry air averages 28.9 g/mol. Water vapor (H2O) has a molar mass of 18 g/mol, making it significantly lighter and more buoyant than CO2 (44), N2O (44), or O3 (48).
Q155. Brittle deformation leads to:
Brittle deformation involves the breaking or fracturing of rock under stress, resulting in joints (fractures with no displacement) and faults (fractures with measurable displacement).
Q156. Evidence of progressive aggradation in a stream channel is the presence of:
Braided channels form when a river carries a high sediment load that exceeds its transport capacity, causing aggradation and channel splitting.
Q157. Consider the following statements: Statement I: the variation of the Earth's magnetic field is stronger during the day than that during the night. Statement II: Magnetic materials become less magnetic on heating.
Both statements are true. However, diurnal variations in Earth's magnetic field are caused by solar wind interacting with the ionosphere, not by the heating of magnetic rocks.
Q158. Crustal thickness, either under continents or oceans, can be determined by:
Both seismic reflection (tracing echoes off the Moho) and seismic refraction (tracing critically refracted waves along the Moho boundary) are standard geophysical methods used to determine crustal thickness.
Q159. What is the most common anion in river water?
Bicarbonate (HCO3-) is the most abundant anion in river water globally, primarily produced by the chemical weathering of carbonate and silicate rocks by carbonic acid.
Q160. Which one of the listed minerals is formed during weathering of rocks on the surface of the Earth?
Bauxite is an aluminum-rich ore formed by intense lateritic (chemical) weathering of surface rocks in tropical climates. The other minerals are primary igneous/metamorphic minerals.