Which of the following allotropes of carbon is used as a lubricant?
A. Coal
B. Graphite
C. Diamond
D. Fullerene
Answer: Option B
Solution (By JKSSB Mock Tests)
Graphite's layered structure with weak van der Waals forces between layers allows them to slide over each other, making it a good dry lubricant. It is used in machines where oil cannot be used (high temperature) or in pencil lead mixed with clay. Diamond is hard, used as abrasive. Fullerenes are nanomaterials, not lubricants. Coal is fuel.
Explanation:
Global warming, caused by increased greenhouse gases, leads to melting of polar ice, thermal expansion of oceans, rise in sea level, and changes in weather patterns (climate change). It does not cool the Earth or decrease CO₂.
Explanation:
Froth flotation is used to concentrate sulfide ores. Galena (PbS) is a sulfide ore; it is wetted by oil (pine oil) and comes to the surface with froth, while gangue particles wetted by water settle down. Bauxite (Al₂O₃·2H₂O) is an oxide ore concentrated by leaching (Bayer's process). Magnetite (Fe₃O₄) is magnetic ore separated by magnetic separation. Carnallite (KCl·MgCl₂·6H₂O) is a halide ore.
Explanation:
2NaHCO₃ (heat) → Na₂CO₃ + CO₂ + H₂O. This is used in baking as CO₂ causes dough to rise. The sodium carbonate formed gives a bitter taste if excess soda is used, hence baking powder (with acid) is preferred.
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