Question

Which of the following are pure substances?
(i) Soda water

(ii) Blood

(iii) Liquid mercury

(iv) Chalk

• A. (i), (iii) and (iv)
• B. (iii) and (iv)
• C. (i) and (iv)
• D. (iv) only

Answer 1

The correct option is B

(iii) and (iv)

Pure substance:

1. It is made up of only one kind of atom.
2. A pure material cannot be divided into different types of matter by physical processes.
3. Elements: It is made up of a single type of atom which can't be broken further. Example: Argon $\left(\mathrm{Ag}\right)$.
4. Compound: It is a pure substance made up of two or more elements chemically combines with one another in a fixed proportion by mass. Example: Sodium hydroxide$\left(\mathrm{NaOH}\right)$.

The explanation for the correct option.

Liquid mercury:

1. Mercury $\left(\mathrm{Hg}\right)$ is an element which is made up of a single type of atom.
2. It is a metal which remains in a liquid state at room temperature.

Chalk:

1. Chalk is a pure substance. It is pure calcite.
2. It is made up of calcium carbonate $\left({\mathrm{CaCO}}_3\right)$.

Since both liquid mercury and chalk are pure substances thus option (b) is the correct option.

The explanation for incorrect options:

Blood:

1. Blood is a colloidal solution.
2. A solution in which the size of solute particles is intermediate between those in true solution and suspension is called a colloidal solution.
3. Blood is made up of several components such as cells, minerals, proteins, water, and so on.

Soda water:

1. It is the solution of water $\left({\mathrm{H}}_2\mathrm{O}\right)$ and carbon dioxide $\left({\mathrm{CO}}_2\right)$.
2. Since the composition is variable and no chemical bonds are involved.
3. Thus, it is a mixture.

Since the soda water and blood are not pure substances thus options (a), (c) and (d) is incorrect.

Hence option (b) is correct, liquid mercury and chalk are pure substances.