Question

Which of the following statements are true for pure substances?
(i) Pure substances contain only one kind of particles
(ii) Pure substances may be compounds or mixtures
(iii) Pure substances have the same composition throughout
(iv) Pure substances can be exemplified by all elements other than nickel

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

Answer 1

The correct option is B

(i) and (iii)

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$\left(\mathrm{NaOH}\right)$.
5. The substances have fixed boiling and melting points.
6. A pure substance usually participates in a chemical reaction to form predictable products.

The explanation for correct options: option b

Pure substances contain only one kind of particle:

1. Pure substances are mostly homogeneous in nature containing only one type of atom or molecule.
2. It consists of a single type of particle and is the same in chemical nature.

Pure substances have the same composition throughout:

These substances mainly have a constant or uniform composition throughout.

Since both the statements are correct thus option (b) is correct.

The explanation for incorrect options:

Pure substances may be compounds or mixtures:

1. Pure substances include both elements and compounds.
2. A mixture is not a pure substance as it consists of two or more pure substances (elements or compounds) mixed together in any proportion so that components do not lose their identity.

Pure substances can be exemplified by all elements other than nickel:

Nickel is an element thus it's a pure substance.

Since the above two statements are incorrect thus options (a), (c), and (d) are incorrect.

Hence, option (b) is the correct option.