Question

Which of the following is not a compound.
A. Sulphur dioxide
B. Chalk
C. Lead
D. Sulphuric acid

Answer 1

A compound is a pure substance containing two or more than two elements combined in a fixed proportion by weight and which can be decomposed into its constituent elements by suitable chemical methods.

Complete step by step answer: If we discuss the option A i.e. sulphur dioxide, it is formed by the chemical combination of sulphur and oxygen in a fixed proportion by weight. The ratio of the mass of sulphur and oxygen is 32:32 i.e. 1:1. Hence it is an example of a compound.
If we talk about option B i.e. chalk, the chemical formula for chalk is $CaC{O_3}$ and is made up of calcium, carbon and oxygen in a fixed proportion by mass. Hence it is also an example of a compound.
If we talk option C i.e. lead, it is an element present in its pure form so it is a single homogeneous identity. So it is not considered to be a compound.
If we talk about option D i.e. sulphuric acid, again it is a compound because it is formed by the combination of hydrogen, sulphur and oxygen in a fixed proportion by weight.
Hence the correct answer is option C.

Note:
All the compounds may be classified into the following two categories:
-Organic compound: These are compounds containing carbon and a few other elements like hydrogen, oxygen, nitrogen sulphur, halogen etc. These were originally obtained only from animals and plants.
-Inorganic compound: These are usually obtained from mineral and rock and contain two or more elements out of more than 110 elements known so far.