Ferromagnetism and crystal structure: sodium vs. iron (ferrous) Assertion (A): Both sodium and ferrous (iron) are ferromagnetic. Reason (R): Both sodium and ferrous have a body-centred cubic (BCC) structure.

Introduction / Context:
Magnetic ordering (ferromagnetic, paramagnetic, etc.) depends on electronic configuration and exchange interactions, while crystal structure can influence but does not alone determine ferromagnetism. This assertion–reason item contrasts sodium and iron at room temperature.

Given Data / Assumptions:

• Sodium (Na) at room temperature: metallic, weakly paramagnetic.
• Iron (Fe) at room temperature: ferromagnetic (α-Fe, BCC).
• Crystal structures: Na is BCC; α-Fe is also BCC at room temperature.

Concept / Approach:

The assertion claims both are ferromagnetic; this is false because sodium is not ferromagnetic. The reason states both have BCC structure; that is true for Na and α-Fe. However, having BCC does not guarantee ferromagnetism (e.g., many BCC metals are not ferromagnetic). Thus the correct logical combination is A false, R true.

Step-by-Step Solution:

Verification / Alternative check:

Empirical data show Curie temperature of iron is well above room temperature (∼1043 K), ensuring ferromagnetism. Sodium shows Pauli paramagnetism with no long-range ordering.

Why Other Options Are Wrong:

(a) and (b) wrongly treat assertion as true; (c) makes R false; (e) denies the true structural statement.

Common Pitfalls:

Assuming crystal structure alone dictates magnetic order; electronic structure and exchange dominate the outcome.

Final Answer:

A is false but R is true