1.

The number of unit cells in 8gm of an element X (atomic mass 40) which crystallizes in bcc pattern is (NA is the Avogadro number) (a) 6.023 x 1023 (b) 6.023 x 1022 (c) 60.23 x 1023(d) \(\Big(\frac{6.023\times10^{23}}{8\times40}\Big)\)

Answer»

(b) 6.023 x 1022

In bcc unit cell, 2 atoms = 1 unit cell

Number of atoms in 8g of element is, Number of moles = \(\Big(\frac{8g}{40g,mol^{-1}}\Big)\) = 0.2 mol

1 mole contains 6.023 x 1023 atoms 0.2 mole contains 0.2 x 6.023 x 1023 atoms

\(\Big(\frac{1\,unitcell}{2\,atoms}\Big)\)0.2 x 6.023 x 1023 = 6.023 x 1022 unit cells



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