Silicon doped with electron rich impurity forms -

1. p-type semiconductor.

2. n-type semiconductor.

3. Intrinsic semiconductor.

4. Insulator.

HINT: It is n-type semiconductor.
Explanation: Silicon doped with electron rich impurity such as phosphorus forms a n-type semiconductor. This is due to presence of mobile electron.
Silicon doped with electron - rich impurity forms .

Thus, option 2 is the correct answer.