According to the band theory of solids, a semiconductor has a valence band and a conduction band separated by a gap, known as energy band gap. Pure semiconductors are called intrinsic semiconductors. At room temperature, some electrons from the valence band can acquire enough energy to cross the band gap and enter the conduction band. The number of conduction electrons is equal to the number of holes is an intrinsic semiconductor. The number of charge carriers can be changed by doping of a suitable impurity in a pure semiconductor. Such semiconductors are known as extrinsic semiconductors. These are of two types (n-type and p-type). A p-n junction is the basic building block of semiconductor devices. Two important processes occur during formation of a p-n junction : diffusion and drift. A 'depletion layer' is formed in a p-n junction. This is responsible for a junction potential barrier. A semiconductor diode is basically a p-n junction with metallic contacts provided at the ends for the application of an external voltage. A diode can be forward-biased or reverse-biased. The barrier height and the depletion layer width in a p-n junction changes depending on the nature of the biasing. (i) (a) Which of the following statements is not true ? (A) The resistance of an intrinsic semiconductor decreases with the increase of temperature. (B) Doping pure $ ext{Si}$ with trivalent impurities gives p-type semiconductors. (C) The majority charge carriers in n-type semiconductors are holes. (D) A p-n junction can act as a semiconductor diode. OR (b) In an unbiased p-n junction : (A) the diffusion current is zero everywhere. (B) the drift current is zero everywhere. (C) the electric potential is zero everywhere. (D) the drift current and the diffusion current cancel each other.