Which of the following element is used in photoelectric cell?

The resistance of conductivity cell filled with 0.1 M KCl solution is 100 ohm and conductivity is $1.70 \times 10^{-4} \mathrm{~S} \mathrm{~cm}^{-1}$. What is the cell constant of the cell?

What type of hybridisation is involved in central atom of hydrides of group 16 elements?

Which from following compounds is used to prepare a refrigerant R-22?