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NCERT Solutions for Class 9th Science Chapter 9 .6 Properties of the Ionic and the Covalent Compounds — In-text Questions

Book page 1789 Updated on2026-09-08

Q1.
Other covalent compounds, such as camphor and naphthalene, also do not conduct electricity. Can you give a reason?
Answer

Because they contain no charged particles that are free to move — neither ions nor free electrons.

A current is nothing but charge in motion. For a substance to conduct, it must supply mobile charge carriers. Camphor and naphthalene supply none:

  • They are made of electrically neutral molecules. Every electron in them is either locked in a shared pair inside a covalent bond or sitting as a lone pair on an atom — none of them can wander off through the solid.
  • They are insoluble in water, so they never get the chance to release ions into solution the way sodium chloride does.
  • Even when melted, they stay as molecules. Melting camphor loosens the molecules from one another, but it does not break the covalent bonds inside them, so still no ions appear.
Why it happens: compare the three cases side by side — a metal conducts because it has free electrons; molten or dissolved sodium chloride conducts because it has free ions; camphor has neither, so the circuit stays broken and the bulb never glows.
Q2.
Predict whether ionic and covalent compounds would conduct electricity in the molten state (the melted state of a substance).
Answer

Ionic compounds conduct in the molten state; covalent compounds do not.

StateIonic compound (e.g. NaCl)Covalent compound (e.g. naphthalene)
SolidDoes not conduct — ions fixed in the latticeDoes not conduct — no ions at all
MoltenConducts — lattice breaks, ions move freelyDoes not conduct — still neutral molecules
Aqueous solutionConducts — ions separated by waterDoes not conduct (if it dissolves at all)

Reasoning for the ionic case. In a solid ionic compound the Na⁺ and Cl⁻ ions are already charged, but they are locked in fixed positions by strong electrostatic forces. Heat the solid past its melting point and those positions break down: the ions are still charged, but now they can move. Charge that can move is a current, so the compound conducts.

Reasoning for the covalent case. Melting a covalent solid separates the molecules from one another, but the covalent bonds inside each molecule survive. The liquid is a crowd of neutral molecules, and neutral particles cannot carry a current.

Why it happens: conduction needs two things at once — charge and mobility. Solid NaCl has the charge but not the mobility; molten naphthalene has the mobility but not the charge; molten NaCl has both, and only it conducts.
Did you know? Aluminium is extracted industrially by passing a current through molten aluminium oxide. The process works only because the melt is full of free Al³⁺ and O²⁻ ions — exactly the prediction you have just made.
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