When Silicon is doped with an electron-rich impurity, for example, an element from Group 15 like Phosphorous and Arsenic, which has 5 valence electrons, some of the electrons will occupy some of the lattice sites in the silicon crystal. Four out of the five will form covalent bonds with the four neighbouring silicon atoms, while the remaining electron becomes delocalized and increases the conductivity of the silicon. The increase in the conductivity is caused due to increase in negative charge and thus the doped silicon is called n-type semiconductor. The correct answer is (ii).