Classification Of Solids

Step 1: Understanding the Concept:
NaCl has a rock salt structure.

Step 2: Detailed Explanation:
NaCl crystallizes in a face-centred cubic (FCC) lattice. Cl ions form an FCC arrangement, and Na ions occupy all octahedral voids. Coordination number is 6:6.

Step 3: Final Answer:
Face centred cubic

Concept: Doping pure intrinsic semiconductor with impurities gives extrinsic semiconductor.

Step 1: Nature of dopant. Arsenic (As) is Group 15 — pentavalent impurity (5 valence electrons).

Step 2: Effect on germanium. Ge has 4 valence electrons. As forms 4 bonds, leaving one extra free electron → n-type semiconductor.

Step 3: Conclusion. Doping changes intrinsic → extrinsic semiconductor (n-type).

Concept: Semiconductors have conductivity between conductors and insulators.

Step 1: Identify common semiconductor elements. Si and Ge belong to Group 14 (p-block).

Step 2: Consider compound semiconductors. GaAs, InP, CdS — combinations of p-block elements.

Step 3: Eliminate other options. Intrinsic/extrinsic refer to types, not source; mixed conductor is unrelated.