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

What type of mixture is an alloy? Explain.

Which of the following is an example of a heterogeneous mixture?

Which of the following substances consists of only one element?

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 $.........$

Explain the concept of a compound.