Which non-metal is a good conductor of electricity?
A. Phosphorus
B. Iodine
C. Graphite
D. Sulphur
Answer: Option C
Solution (By JKSSB Mock Tests)
Graphite, an allotrope of carbon, is a good conductor of electricity. This is because each carbon atom is bonded to three others, leaving one free valence electron per atom that is delocalized and can move freely between the layers to conduct electricity, unlike diamond which is an insulator.
Explanation:
Modern periodic law: The physical and chemical properties of elements are periodic functions of their atomic numbers. This was established by Moseley. Mendeleev's periodic law was based on atomic masses. Atomic number (Z) determines electronic configuration, which determines chemical behavior. Mass numbers vary with isotopes.
Explanation:
Niels Bohr in 1913 proposed the planetary model where electrons revolve in certain allowed circular orbits without radiating energy, with quantized angular momentum. Rutherford proposed the nuclear model but did not specify quantized orbits. Thomson gave plum pudding. Chadwick discovered neutron.
Explanation:
Fractional distillation is used when the boiling points differ by less than 25 K. A fractionating column provides repeated condensation–vaporization cycles, improving separation. Example: separation of petrol, kerosene from crude oil. Simple distillation works if difference > 25 K. Separating funnel separates immiscible liquids. Crystallization purifies solids. Exam note: Fractionating column packed with glass beads increases surface area.
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