Which from following combinations is an example for construction of n-type semiconductor?

Calculate the density of metal having molar mass $$210 \mathrm{~g} \mathrm{~mol}^{-1}$$ that forms simple cubic unit cell. $$\left(\mathrm{a}^3 \cdot \mathrm{N}_{\mathrm{A}}=21.5 \mathrm{~cm}^3 \mathrm{~mol}^{-1}\right)$$

Which element from following rapidly loses its luster in air and tarnishes?

A neon-dioxygen mixture contains $$64 \mathrm{~g} \mathrm{~O}_2$$ and $$160 \mathrm{~g} \mathrm{~Ne}$$. If the total pressure is $$25 \mathrm{~bar}$$, calculate the partial pressure of dioxygen.