The Resistivity of Iron at 20ºC Is 10 $\times$ 10^-8 $\Omega$ · M and the Number of Electrons Per Cubic Centimeter

Multiple Choice

The resistivity of iron at 20ºC is 10 $\times$ 10^-8 $\Omega$ · m and the number of electrons per cubic centimeter is 17.0 $\times$ 10²².If you take the average speed of the electrons to be equal to their root-mean-square speed (at T = 300 K) of 1.17 $\times$ 10⁵ m/s,it follows that their mean free path, $\lambda$ ,must be

A) 0.245 nm
B) 0.317 nm
C) 0.428 nm
D) 0.556 nm
E) None of these is correct.