The S.I. unit of electron mobility is :

The correct answer is Option (2) → m²/V s

Mobility is the drift velocity per unit electric field:

    \( \displaystyle \mu = \frac{v_d}{E} \)

Putting in the units of drift velocity (\( \mathrm{m\,s^{-1}} \)) and of electric field (\( \mathrm{V\,m^{-1}} \)):

    \( \displaystyle [\mu] = \frac{\mathrm{m\,s^{-1}}}{\mathrm{V\,m^{-1}}} = \frac{\mathrm{m^{2}}}{\mathrm{V\,s}} \)

So the SI unit of mobility is \( \mathrm{m^{2}\,V^{-1}\,s^{-1}} \).

NCERT (2026-27):
Mobility – “… An important quantity is the mobility μ defined as the magnitude of the drift velocity per unit electric field:

    \( \displaystyle \mu = \frac{|\mathbf{v}_d|}{E} \qquad (3.24) \)

The SI unit of mobility is m²/Vs and is 10⁴ of the mobility in practical units (cm²/Vs).”