c
અહીં,\( r = 0.5 Å, d = 2r = 1 Å = 10-10 m, \)
\(T = 0 °C = 273 K, P = 1 atm = 1.01 \times  10^5 Nm^{-2}\)

સરેરાશ મુક્ત પથ \(\,\bar l\,\, = \,\,\frac{1}{{\sqrt 2 n\pi {d^2}}}\) અને 

\(n\, = \,\frac{P}{{{k_B}T}}\) પરથી \(\bar l\,\, = \,\,\frac{{{k_B}T}}{{\sqrt 2 n\pi {d^2}}}\,\,\,\)

\( = \frac{{1.38 \times {{10}^{ - 23}} \times 273}}{{\sqrt 2  \times 3.14 \times 1.01 \times {{10}^5} \times {{10}^{ - 20}}}}\,\,\, \)

\(= 8.425 \times {10^{ - 7}}\,\,m\,\,\, = 8425 \times {10^{ - 10}}\,\,m\,\, = \,8425\mathop A\limits^ \circ  \)