Nature of Matter: Elements, Compounds, and Mixtures — Important Questions

Nitrogen, oxygen, argon, carbon dioxide, and water vapour

Air is a uniform mixture made mainly of nitrogen, oxygen, argon, carbon dioxide, and water vapour. Nitrogen is the largest component, about 78% of air, and it does not take part in combustion. Dust particles may be present in air, but they are not treated as major components of air.

Cannot be broken down into simpler substances, Are building blocks of all matter, Made up of identical atoms

Elements are the simplest substances that cannot be broken down further, serve as building blocks of matter, and consist of identical atoms. However, some elements like hydrogen and oxygen exist as molecules, not single atoms.

Carbon dioxide

Lime water turns milky when it reacts with carbon dioxide to form calcium carbonate (white precipitate). This is a standard test for detecting carbon dioxide in air.

Stainless steel, Brass, Bronze

Alloys are uniform mixtures of metals. Stainless steel (iron + nickel + chromium), brass (copper + zinc), and bronze (copper + tin) are all alloys. Pure gold and pure iron are elements, not alloys.