Verified Solution • 2025–26 Session moderate

QNEET-2018-Ch-853: NEET 2018 Chemistry - Class 12 NEET-2018-Ch-853 Solution: Iron exhibits bcc structure at room temperature. Above \(900^…

Iron exhibits bcc structure at room temperature. Above 900∘C900^\circ C it transforms to fcc structure. The ratio of density of iron at room temperature to that at 900∘C900^\circ C (assuming molar mass and atomic radii of iron remains constant with temperature) is 32\frac{\sqrt{3}}{\sqrt{2}} 4332\frac{4\sqrt{3}}{3\sqrt{2}} 3342\frac{3\sqrt{3}}{4\sqrt{2}} 12\frac{1}{2}

Multiple Choice Options

  • A 32{{\sqrt 3 } \over {\sqrt 2 }} 2 _ 3 _ _
  • B 4332{{4\sqrt 3 } \over {3\sqrt 2 }} 3 2 _ 4 3 _ _
  • C 3342{{3\sqrt 3 } \over {4\sqrt 2 }} 4 2 _ 3 3 _ _
  • D 12{1 \over 2} 2 1 _

Step-by-Step Verified Solution

Density ( _ ) = Z _ M w N A _ V For bcc lattice : Z = 2, r = 3 a 4 _ V = 4 3 � r 3 = 4 3 � ( 3 a 4 ) 3 = 4 3 � _ 3 3 _ a 3 64 = 3 � a 3 16 For fcc lattice : Z = 4, r = 3 a 2 2 _ V = 4 3 � r 3 = 4 3 � ( a 2 2 ) 3 = 4 3 � _ a 3 8 _ 2 2 = � a 3 12 2 b c c f c c = _ 1 _ 2 = Z 1 _ V 2 V 1 _ Z 2 _ _ 1 _ 2 = 2 _ 3 � a 3 16 4 _ � a 3 12 2 = 2 _ 3 _ 2 _ 12 4 _ 16 = 3 3 4 2

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