MHT CET · Chemistry · Solid State

Sodium crystallises in bcc structure with radius \(1 \cdot 86 \times 10^{-8} \mathrm{~cm}\). Calculate the edge length of unit cell?

A \(4.29 \times 10^{-8} \mathrm{~cm}\)
B \(6 \cdot 20 \times 10^{-8} \mathrm{~cm}\)
C \(8 \cdot 05 \times 10^{-8} \mathrm{~cm}\)
D \(3 \cdot 72 \times 10^{-8} \mathrm{~cm}\)

Verified Solution

Answer & Solution

Correct Answer

(A) \(4.29 \times 10^{-8} \mathrm{~cm}\)

Step-by-step Solution

Detailed explanation

For bcc unit cell, \(r=\frac{\sqrt{3} a}{4}\)
\(\therefore \quad \mathrm{a}=\frac{4 \mathrm{r}}{\sqrt{3}}=\frac{4 \times 1.86 \times 10^{-8} \mathrm{~cm}}{1.732}=4.29 \times 10^{-8} \mathrm{~cm}\)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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