Which of the following is an exception in terms of its life cycle?

In the conversion of a zinc ore to zinc metal,the process of roasting involves:

The refracting angle of a prism is $A$ and the refractive index of the material of the prism is $\cot (A / 2)$. The angle of minimum deviation of the prism is

The position vector of a point lying on the line joining the points whose position vectors are $\hat{i}+\hat{j}-\hat{k}$ and $\hat{i}-\hat{j}+\hat{k}$ is:

The compound,found in nature in gas phase but ionic in solid state is

Which one has the highest boiling point?