Question

If an element X forms FCC cubic structure, then
the number of unit cells of X in 100 g of the
crystal is (Atomic mass of X = 50 u)
(1) 6.02 x 1023 (2) 3.01 1023
(3) 6.02 x 1022 (4) 3.01 x 1024​

Answer 1

The correct answer is (2) i.e 3.01 * 10^23.

1) Since, the given mass is 100 g and he atomic mass of the element X is 50 u.

So, the given number of moles of the element X is 2 moles.

2) 2 moles means there are 2* 6.022*10^23 atoms of element X present.

3) One unit cell in FCC Cubic structure requires 4 atoms.

4) So, the number of unit cells present in 100 g of element X is given by:

    ( 2* 6.022*10^23 )/4 = 3.01 * 10^23 atoms.