First slide
Density of unit cell
Question

Iron exhibits bcc structure at room temperature. Above 900°C, it transforms to fcc structure. The ratio of density of iron at room temperature to that at 900°C (assuming molar mass and atomic radii of iron remains constant with temperature) is

Moderate
Solution

 For bcc lattice :Z=2,a=4r3

 For fcc lattice :Z=4,a=22rdR.T.d900°C=ZMNAa3bccZMNAa3fcc

Given, molar mass and atom radii are constant.

=2422r4r33=3342

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