Mass number of silicon is

Q. The ratio of the neutrons present in nitrogen atom and a silicon atom is:

Q. Assertion :The number of electrons in a p-type silicon semiconductor is less than the number of electrons in a pure silicon semiconductor at room temperature. Reason: It is due to law of mass action.

Q. What mass of phosphorous is needed to dope $1.0\text{g}$ of silicon so that the number density of conduction electrons in the silicon increased by a multiply factor of ${10}^6$ from the ${10}^{16}{\text{m}}^{-3}$ in pure silicon.
(Take the concentration of silicon atoms $n_{\text{Si}}=5\times {10}^{28}{\text{m}}^{-3}\text{Molar mass of silicon}{M}_{\text{Si}}=28.1\text{g}\text{Molar mass of phosphorous}{M}_{\text{P}}=30.97\text{g}\text{Avogadro number}{N}_A=6.023\times {10}^{23})$

Q. An atom of silicon has a mass number of $29$. How many neutrons does it have?