Q.homogeneous mixture
Concept understanding — Classification of Matter
Matter is anything that has mass and occupies space. To make sense of the huge variety of matter around us, chemists classify it in two independent ways: by physical state and by chemical composition.
By physical state: matter exists as a solid (fixed shape and volume), a liquid (fixed volume, takes the container's shape) or a gas (neither fixed shape nor fixed volume). These are not permanent labels -- the same substance moves between states as temperature and pressure change (e.g. ice → water → steam).
By chemical composition: matter splits into mixtures and pure substances.
- A mixture contains two or more chemical entities together with no chemical reaction between them, so each component keeps its own properties and can (in principle) be separated physically. Mixtures are further split by appearance into homogeneous (uniform throughout, e.g. a salt solution) and heterogeneous (visibly made of distinguishable parts, e.g. oil and water).
- A pure substance contains only one kind of atom or molecule, and splits into:
- Elements -- one type of atom only, existing as monatomic units (e.g. gold Au) or polyatomic units (e.g. hydrogen H₂, sulphur S₈).
- Compounds -- molecules containing two or more atoms of different elements chemically bonded, with properties completely unlike their constituent elements (e.g. sodium chloride, formed from reactive sodium metal and toxic chlorine gas, is a stable, biologically essential crystalline solid).
Matter has two independent classification axes: physical state (solid/liquid/gas) and chemical composition (mixture vs. pure substance, with pure substances splitting further into elements and compounds).
A homogeneous mixture is uniformly blended throughout.
A salt solution (salt dissolved uniformly in water).
Step 1. A homogeneous mixture has its components blended uniformly throughout the entire sample, so any portion of it has the same composition.
Step 2. A solution of common salt in water is a standard example — the dissolved salt is evenly distributed throughout the water.
A salt solution (salt dissolved uniformly in water).
Recall the definition of a homogeneous mixture and give a familiar solution as the example.
- Giving an example that is actually a compound (like water itself) rather than a mixture of two or more substances.
- CBSE 2026Set sz1 markMCQQ.Select the correct one: A pure substance which contains only one type of atoms is called(a) An element(b) A Compound(c) A Solid(d) A liquid
›Reveal solutionSolution
A pure substance containing only one type of atom is classified as an element; this is a statement about chemical composition, not physical state.
Pure substances are classified into elements and compounds based on their composition:
- An element is a form of matter that cannot be broken down into simpler substances by chemical means and consists of only one kind of atom (e.g. Na, Cu, O2, S8 — all atoms of the same type, though they may combine as molecules of that one element).
- A compound is formed when two or more different elements combine chemically in a fixed ratio (e.g. H2O, NaCl).
- 'Solid' and 'liquid' are physical states of matter and say nothing about how many kinds of atoms are present — a solid or liquid can be an element (solid Fe, liquid Br2) or a compound (solid NaCl, liquid H2O).
Since the question specifically describes 'only one type of atoms', this is the defining property of an element.
✓Final answerThe correct option is (a) An element.
- CBSE 2024Set ANNUAL1 markMCQQ.Assertion (A): Graphite is an Element. Reason (R): Element is the pure form of substance containing same kind of atoms.(a) Both (A) and (R) are true and (R) is correct explanation of (A).(b) Both (A) and (R) are true and (R) is not the correct explanation of (A).(c) (A) is true but (R) is false.(d) (A) is false but (R) is true.
›Reveal solutionSolution
Graphite consists only of carbon atoms bonded together (it is an allotrope of the element carbon), so it is indeed an element, and this is precisely because it satisfies the definition given in the reason.
Assertion (A): Graphite is a form (allotrope) of carbon, containing only carbon atoms — no other element is combined in it. So graphite is correctly classed as an element (specifically, the element carbon in one of its structural forms).
Reason (R): An element is defined as the purest form of a substance made of only one kind of atom. This is the standard, correct definition, and it is exactly why graphite — being made of only carbon atoms — qualifies as an element.
✓Final answerBoth (A) and (R) are true and (R) correctly explains (A) — option a.
- CBSE 2018Set ANNUAL1 markQ.Write answer in one sentence: Define "Mixture".
›Reveal solutionSolution
A mixture is a physical (not chemical) blend of two or more substances in any proportion; each substance keeps its own identity and can be separated by physical means.
Unlike a compound, where elements combine chemically in a fixed ratio to form a new substance, in a mixture the components are only physically mingled — no new bonds form, and the ratio of components can vary. Examples: air (a mixture of N2, O2, CO2, etc.), salt water, and sand + iron filings. Mixtures can be homogeneous (uniform composition, like sugar solution) or heterogeneous (non-uniform, like sand and water).
✓Final answerA mixture is a physical combination of two or more substances, in any proportion, where each component retains its own properties and can be separated by physical methods.
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