Question

Potassium crystallizes in a body-centered cubic unit cell. The mass of the unit cell is:

• A. $1.29\times {10}^{-23}gm$
• B. $1.295\times {10}^{-22}gm$
• C. $6.2\times {10}^{-23}gm$
• D. $1.29\times {10}^{-24}gm$

Answer 1

The correct option is A $1.29\times {10}^{-23}gm$

$Z=2$ for body centred cubic unit cell.

Molecular weight of unit cell $=39\times 2=78$ $amu$

$78$ $amu=1.29\times {10}^{-23}$ $gm$ $(1$ $amu=1.6726\times {10}^{-24}$ $gm)$