Which of the following allotropes of carbon is used as a lubricant?
A. Diamond
B. Fullerene
C. Graphite
D. Coal
Answer: Option C
Solution (By JKExamLibrary)
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:
Neutron has mass approximately equal to proton (1.675 × 10⁻²⁷ kg) and no electric charge. Proton mass ~1.673 × 10⁻²⁷ kg, positive charge. Electron mass ~9.11 × 10⁻³¹ kg, negative charge. Positron is the antiparticle of electron, same mass, positive charge. Neutron's neutrality makes it important for nuclear stability.
Explanation:
Na₂CO₃ reacts with Ca²⁺/Mg²⁺ to form insoluble CaCO₃/MgCO₃, which are removed. This is permanent hardness removal. Boiling works for temporary hardness. Ion exchange is another method.
Explanation:
The standard reduction potential (E°) indicates the tendency of a species to gain electrons. A higher positive E° value means a greater tendency to be reduced, making it a stronger oxidizing agent. Fluorine (F2) has the highest standard reduction potential (+2.87 V), making it the strongest oxidizing agent among the choices.
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