Question

0.15 mole of a semiconductor material (XY) has a mass of 21.6 g. The electronic configuration of X is $\text{[Noble gas]}n{s}^2(n-1)d^{10}$. The material is doped with an element Z that replaces an exact amount of Y, having electronic configuration $\text{[Noble gas]}n{s}^2(n-1)d^{10}(n-2)p^5$. The metal alone has a packing fraction of 0.74.
Then:

• A. X is cadmium, molar mass 112.4 g/mol, HCP
• B. X is copper, molar mass 63.5 g/mol, HCP
• C. XY - n - type semiconductor
• D. XY - p - type semiconductor

Answer 1

Answer: (A), (C)

The correct options are
A X is cadmium, molar mass 112.4 g/mol, HCP
C XY - n - type semiconductor

Molar mass of $XY=\frac{21.6g}{0.15mol}=144g/mol$
The electronic configuration of X is $\text{[Noble gas]}n{s}^2(n-1)d^{10}$ which can't be $Cu$ since $Cu$ has electronic configuration $\text{[Noble gas]}4s^{1}3d^{10}$. The given configuration suggests $Zn$ family so $Cd$ can be the right canditate as per the option suggests.
Then $Y=144-112.4=31.6g/mol$. So $Y$ could be sulphur (32g/mol) and semiconductor $XY$ could be $CdS$.
The configuration of dopant is $\text{[Noble gas]}n{s}^2(n-1)d^{10}(n-2)p^5$ which is a halogen probably Cl or Br.
Comparing with Y, configuration of $S\to p^4$ and $\text{dopant}\to p^5$.
This makes an n-type semiconductor.
Both CCP and HCP has packing fraction 0.74.