The values of conductivity of some materials at 298.15 K⁻¹ in Sm⁻¹ are 2.1 × 10³,
1.0 × 10⁻¹⁶, 1.2 × 10,3.91,1.5 × 10⁻², 1 × 10⁻⁷, 1.0 × 10³.
The number of conductors among the materials is _____________.

Solution

Chemistry ma’am · 2 steps

Match each number to its NCERT material, then count metals and electrolytes together as conductors.

1. Three classes. Materials are grouped as conductors, semiconductors and insulators. Conductors include both metallic conductors and electrolytic conductors such as acid solutions.

   Conductivity (S m⁻¹)	Material (NCERT table)	Class
   2.1 × 10³	Sodium	conductor
   1.0 × 10³	Iron	conductor
   1.2 × 10	Graphite	conductor
   3.91	0.1 M HCl solution	conductor (electrolytic)
   1.5 × 10⁻²	Silicon	semiconductor
   1 × 10⁻⁷	Copper(II) oxide, CuO	semiconductor
   1.0 × 10⁻¹⁶	Glass	insulator

2. So. Sodium, iron, graphite and 0.1 M HCl are conductors, so the number of conductors is 4.

The common slip: 3. Treating 0.1 M HCl (3.91) as a non-conductor and counting only the solids gives 3. An electrolytic conductor is still a conductor.

The idea to keep. Metals and graphite sit at the top, insulators near 10⁻¹⁶ and below. A strong electrolyte solution like dilute HCl also counts as a conductor, even though its conductivity is only a few S m⁻¹.

Answer from the NTA final answer key. Solution by PrepWiser.