Question

Which of the following is an example of a pure substance?

• A. Chalk powder dissolved in water
• B. Bronze
• C. Soda water
• D. Carbon dioxide

Answer 1

The correct option is D

Carbon dioxide

The explanation for correct option:
(D) Carbon dioxide (CO₂)

• Pure substances are substances that are made up of only one kind of particle and have a fixed or constant structure.
• Pure substances are further classified as elements and compounds.
• An element is a substance that consists of only one type or kind of atom.
• The simplest form of a pure substance made up of only one kind of atom is Element.
• Elements constitute the simplest chemical substances in which all the atoms are exactly the same.
• Elements exist in their simplest form and cannot be broken down further. So, elements can exist in the form of ions, atoms, isotopes, molecules.
• An example of an element is Nitrogen atom(N), Nitrogen gas (N₂), Nitrogen ion(N₃^–) and Nitrogen isotopes (Nitrogen-13, Nitrogen-14, and Nitrogen-15).
• An Example of Pure substance in compounds can be Carbon di oxide, Alcohol etc.

The explanation for incorrect options:
(A) Chalk powder dissolved in water

• This is containing two different things like water and chalk (Calcium carbonate, CaCO₃) so can't be a pure substance.

(B) Bronze

• Bronze is an alloy consisting primarily of copper, commonly with about 12–12.5% tin and often with the addition of other metals
• Hence it is also not pure substance.

(C) Soda water

• Carbonated water is water that has been infused with carbon dioxide gas under pressure.
• This produces a bubbly drink that's also known as sparkling water, club soda, soda water, seltzer water, and fizzy water.

Hence option D is correct.