During the extraction of aluminium by Hall-Héroult process, cryolite (Na₃AlF₆) is added to alumina to:
A. Lower the melting point and increase conductivity
B. Act as catalyst
C. Increase the yield of aluminium
D. Prevent corrosion
Answer: Option A
Solution (By JKSSB Mock Tests)
Alumina has a very high melting point (~2050°C). Cryolite (and fluorspar) is mixed to form a molten mixture with lower melting point (~950°C) and better electrical conductivity, enabling electrolytic reduction. The electrolyte is a solution of alumina in molten cryolite. Carbon anodes are consumed. This reduces energy consumption.
Explanation:
The ozone layer is located in the lower stratosphere (~15-35 km altitude), where ozone concentration is highest. It absorbs harmful ultraviolet radiation (UV-B and UV-C) from the sun. Ground-level ozone (troposphere) is a pollutant and component of smog, harmful to health. Ozone depletion is caused by chlorofluorocarbons (CFCs) which release chlorine atoms that catalytically destroy O₃.
Explanation:
Sodium bicarbonate (NaHCO₃) neutralizes excess stomach acid (HCl) and provides relief from acidity. It is a mild base. NaOH is too strong and corrosive. NaCl is table salt; CaSO₄ is used in plaster of Paris.
Explanation:
James Chadwick discovered the neutron in 1932. It is a neutral particle with mass almost equal to proton. Its discovery explained isotopes' mass differences.
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