Which one of the following is not an element?

Which of the following pairs of elements might form an alloy?

Which of the following contains only one element?

Which method is used to separate a mixture of $KCl$ and $KClO_3$?

$A$ mixture of sodium chloride and ammonium chloride is separated by:

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A:$ $A$ mixture contains benzoic acid and naphthalene. The pure benzoic acid can be separated out by the use of benzene.
Reason $R:$ Benzoic acid is soluble in hot water.
In the light of the above statements,choose the most appropriate answer from the options given below.