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(C) The conductivity of a semiconductor is given by $\sigma = e(n_e \mu_e + n_h \mu_h)$.As the temperature increases,the number density of charge carr

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number density of charge carriers increases,relaxation time decreases,but the effect of the decrease in relaxation time is much less than the increase in number density

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(C) The conductivity of a semiconductor is given by $\sigma = e(n_e \mu_e + n_h \mu_h)$.As the temperature increases,the number density of charge carriers ($n_e$ and $n_h$) increases exponentially according to the relation $n = C T^{3/2} \exp(-E_g / 2kT)$.Although the relaxation time $(	au)$ decreases with an increase in temperature due to increased scattering,the exponential increase in the number density of charge carriers far outweighs the decrease in mobility caused by the reduction in relaxation time.Therefore,the net effect is an increase in the conductivity of the semiconductor.

The conductivity of a semiconductor increases with an increase in temperature because

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Assertion : The resistivity of a semiconductor increases with temperature.
Reason : The atoms of a semiconductor vibrate with larger amplitude at higher temperatures,thereby increasing its resistivity.

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