Question

(a) What is meant by (i) element (ii) Compound and (iii) mixtures? Write down the names of two elements, two compounds and two mixtures.
(b) Classify the following into elements, compounds and mixtures:
Marble, air, gold, Brass, Sand, Diamond, graphite, Petroleum, Common salt, Sea-water, Chalk.

Answer 1

Elements are pure substances that consist of only atoms and have the same number of protons in the atomic nuclei. Compound is the substance that consists of two or more elements in a fixed portion. Mixture is formed by mixing of two or more chemical substances physically.

Complete answer:
Elements are the pure form and consisting of only atoms, they are a total of $118$chemical elements were discovered by scientists. Some of the examples of elements were gold, hydrogen, silver and copper.
Compounds are substances that consist of two or more elements. Some of the examples were sodium chloride, hydrogen chloride.
Mixture is also a chemical substance that is formed by mixing two or more chemical compounds physically. Some of the examples of mixtures are gold ornaments made by mixing gold and copper.
Marble is a mixture. Air is a mixture of several gases. Gold is an element. Brass is a mixture of elements. Sand is also a mixture. Diamond and graphite are mixtures. Petroleum is also a mixture. Common salt is a compound. Sea- water is a mixture. Chalk is a mixture.

Note :
Though diamond and graphite are made up of single atom carbon, these are not made up of single atoms of carbon. Thus, both these are not compounds or elements but come under mixtures. Chalk is made up of different compounds and called a mixture.