Which of the following statements are true about semiconductors?
(i) Silicon doped with an electron-rich impurity is a p-type semiconductor.
(ii) Silicon doped with an electron-rich impurity is an n-type semiconductor.
(iii) Delocalised electrons increase the conductivity of doped silicon.
(iv) An electron vacancy increases the conductivity of the n-type semiconductor.
Option (ii) and (iii) are the answers.