Who first proposed the atomic theory of matter? What does it suggest?

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.

The separation of two coloured substances was done by paper chromatography. The distances travelled by solvent front,substance $A$ and substance $B$ from the base line are $3.25 \ cm$,$2.08 \ cm$ and $1.05 \ cm$ respectively. The ratio of $R_{f}$ values of $A$ to $B$ is $.........$

$A$ mixture of $NH_4Cl$ and $NaCl$ can be separated by

What is the process of converting a solid directly into a gaseous state called?

What type of mixture is an alloy? Explain.