Which of the following is a characteristic property of ionic compounds?
A. They are good conductors of electricity in the solid state.
B. They have low melting and boiling points.
C. They are soluble in non-polar solvents like benzene.
D. They are soluble in water and conduct electricity in molten or aqueous state.
Answer: Option D
Solution (By JKSSB Mock Tests)
Ionic compounds are soluble in polar solvents like water. In the solid state, ions are fixed in a lattice and cannot move, so they don't conduct. However, in molten or aqueous states, the ions become free to move, allowing them to conduct electricity. They generally have high melting points.
Explanation:
Sodium and potassium are highly reactive alkali metals that react vigorously with oxygen and moisture in the air, potentially catching fire. To prevent accidental fires, they are stored immersed in kerosene oil. Magnesium and calcium do not require such extreme storage conditions.
Explanation:
Mendeleev placed Cobalt (atomic mass 58.9) before Nickel (atomic mass 58.7) to maintain chemical similarities, violating his own periodic law based on atomic mass. Isotopes weren't an issue then, and H's position was ambiguous, but the Co/Ni placement is a classic anomaly of his atomic mass-based table.
Explanation:
Water self-ionizes: H₂O ⇌ H⁺ + OH⁻. At 25°C, [H⁺] = [OH⁻] = 10⁻⁷ mol/L, so Kw = 10⁻¹⁴ and pH = pOH = 7. A solution is neutral when [H⁺] = [OH⁻]. pH 7 is neutral only at 25°C; at higher temperatures, Kw increases, pH of neutrality drops but still [H⁺]=[OH⁻].
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