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Chemistry · PYQ NEET UG 2018
हिन्दीIron exhibits bcc structure at room temperature. Above \( 900\text{ }^\circ\text{C} \), it transforms to fcc structure. The ratio of density of iron at room temperature to that at \( 900\text{ }^\circ\text{C} \) (assuming molar mass and atomic radii of iron remains constant with temperature)?
Correct answer · Option 3
\( \frac{3\sqrt{3}}{4\sqrt{2}} \)
Explanation
Density \( d = \frac{Z \times M}{N_A \times a^3} \). For bcc, \( Z=2, a = \frac{4r}{\sqrt{3}} \); for fcc, \( Z=4, a = \frac{4r}{\sqrt{2}} \). Taking the ratio gives \( \frac{3\sqrt{3}}{4\sqrt{2}} \).
