Nature of Matter — IISER Chemistry MCQs with Solutions

Solution: Air is a homogeneous mixture precisely because its component gases are uniformly distributed and its composition is uniform throughout — exactly what R states. So both A and R are true and R correctly explains A.

Solution: A compound has a fixed, definite composition, but a mixture has a variable composition because its components are only physically combined and can be present in any ratio (R). R correctly explains why a mixture, unlike a compound, has a variable composition, so both are true and R explains A.

Solution: A substance with a fixed composition whose constituents can be separated only by chemical means (here, electrolysis) — and not by physical methods — is a compound. An element cannot be broken down into simpler substances at all, and a mixture has a variable composition and separates by physical methods.

Solution: A compound contains two or more different elements in a fixed ratio: only water (H₂O) and carbon dioxide (CO₂) qualify — that is 2. Copper and oxygen are elements (one type of atom each), while air and the sugar solution are mixtures. So exactly two of the six are compounds.

Solution: In a gas the particles are far apart compared with solids and liquids, leaving large empty spaces that can be reduced on compression. In solids and liquids the particles are already close together, so they strongly resist compression. Gas particles are not heavier, are not rigidly arranged, and in fact move easily and fast.

Solution: A salt–sugar mixture is heterogeneous because its composition is not uniform and the two solids can be distinguished. R states exactly this defining feature of a heterogeneous mixture, so both statements are true and R correctly explains A.

Solution: Set the two readings equal: x = (9/5)x + 32 ⇒ x − (9/5)x = 32 ⇒ −(4/5)x = 32 ⇒ x = −40. So −40 °C equals −40 °F — the only temperature that is numerically the same on both scales.