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1)

 Sodium metal crystallises in a body centred cubic lattice with a unit cell edge of 4.29 Å. The radius of sodium atom is approximately


A) 1.86 Å

B) 3.22 Å

C) 5.72 Å

D) 0.93 Å

Answer:

Option A

Explanation:

2622021716_m41.JPG

From this figure

      (AC)2=(AB)2+(BC)2

     (AC)2=a2+a2=2a2

  Also,         (AD)2=(AC)2+(DC)2

               (4r)2=(2a)2+a2

      16r2=3a2

   r=34a

Now, when Na metal crystallise in bcc unit cell with unit cell edge, a= 4.29Å

   We have the formula for radius

i.e,            r=34×4.29 Å  =1.86Å