Out of the following impurities, which impurity is not a trivalent?

In the energy band diagram of a material shown below,the open circles and filled circles denote holes and electrons respectively. The material is

For a pure $Si$ crystal at $300 \ K$,the electron $(n_e)$ and hole $(n_h)$ concentrations are equal,being $1.5 \times 10^{16} \ m^{-3}$. On doping with Indium,the hole concentration increases to $4.5 \times 10^{22} \ m^{-3}$. Calculate the new electron concentration $(n_e)$ in the doped $Si$.

Which of the following statements is true for an $N$-type semiconductor?

In an $n$-type semiconductor:

If the number of holes and electrons are represented by $n_h$ and $n_e$ respectively,then which of the following is correct for an intrinsic semiconductor?