Which element exists as a solid at $25\,^{\circ}C$ and $1$ atmospheric pressure among the following?

Which one of the following is not an element?

$A$ mixture of sand and sulphur may best be separated by:

You have a mixture of three liquids $A$,$B$,and $C$. There is a large difference in the boiling points of $A$ and the rest of the two liquids,i.e.,$B$ and $C$. The boiling points of liquids $B$ and $C$ are quite close. Liquid $A$ boils at a higher temperature than $B$ and $C$,and the boiling point of $B$ is lower than that of $C$. How will you separate the components of the mixture?

What is an element?

Name a suitable technique for the separation of the components from a mixture of calcium sulphate and camphor.