The temperature of an ideal gas in three dimensions is 300K . The...

$k = 1 . 38 \times {10}^{- 23}J{K}^{- 1}$

Mass of electron $= 9 \times {10}^{- 31}kg$

$⇒ {\lambda}_{D} = \dfrac{h}{\sqrt{2m \times \dfrac{3}{2} \times kT}}$$= \dfrac{h}{\sqrt{3mkT}}$

$⇒ {\lambda}_{D} = \dfrac{6 . 6 \times {10}^{- 34}}{\sqrt{3 \times 9 \times {10}^{- 31} \times 1 . 38 \times {10}^{- 23} \times 300}} = \dfrac{6 . 6 \times {10}^{- 34}}{105 . 72 \times {10}^{- 27}} = 62\overset{ο}{A}$

Thus $x = 62\overset{ο}{A}$