# NEET Chemistry The Solid State Questions Solved

BOARD

An element occurs in bcc structure. It has a cell edge length of 250 pm. Calculate the molar mass if its density is 8.0 g cm-3. Also calculate the radius of an atom of this element.

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Concept Questions :-

Density/Formula/packing fraction/ Semiconductors

Given : For bcc structure, Z = 2

Edge of the unit cell, a = 250 $\rho$m

Density of the element, $\rho$ = 8.0 g/cm3

M = ?      r = ?

Using the formula

$\rho$ = $\frac{Z×M}{{a}^{3}×{N}_{0}}$ $⇒$M = $\frac{\rho ×{a}^{3}×{N}_{0}}{Z}$

$⇒$M =

$⇒$M = $\frac{752750000×{10}^{-7}}{2}$ $\therefore$ M = 37.6 g mol-1

For, bcc, a = $\frac{4r}{\sqrt{3}}$     $⇒$250 = $\frac{4r}{\sqrt{3}}$

$\therefore$  r = $\frac{250×1.73}{4}$ = 108.25 pm

Difficulty Level:

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