Mobility $\mu=\dfrac{v_d}{E}=\dfrac{e\tau}{m}$, where $\tau$ is the average relaxation time (time between collisions) and $m$ is the mass of the charge carrier.

$\mu$ does not depend on the applied field $E$ (it's a proportionality constant, ruling out A). It clearly depends on mass $m$ (ruling out C). As temperature increases, collisions become more frequent, so $\tau$ decreases, and hence $\mu$ decreases.

Answer: (B) Mobility decreases with increase in temperature