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For Class 8, 9 & 10

Foundation - a strong base in Physics, Chemistry, Maths & Biology

Concept-first questions with clear model answers across all four subjects, aligned to NCERT. Start early, build the habit, and walk into your board exams, NEET and JEE already ahead.

Class 824Class 924Class 1036
SubjectAllPhysics 19Chemistry 19Biology 19Mathematics 27
ChapterAllAtoms and MoleculesForce and Laws of MotionGravitationHeron's FormulaImprovement in Food ResourcesIs Matter Around Us PureLinear Equations in Two VariablesMatter in Our SurroundingsMotionNatural ResourcesNumber SystemsPolynomialsSoundStatisticsStructure of the AtomSurface Areas and VolumesThe Fundamental Unit of LifeTissuesWork and Energy

Showing 1 question for Class 9. Tap a card to reveal the answer.

ChemistryAtoms and Moleculesmedium

State the law of conservation of mass with an example.

Reveal answer ↓

What it is

In any chemical reaction the total mass stays the same - atoms are only rearranged, never lost.

Answer

The law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction; the total mass of the reactants equals the total mass of the products. For example, when 12 g of carbon burns completely in 32 g of oxygen, exactly 44 g of carbon dioxide is formed (12 + 32 = 44).

mass of reactants = mass of products

  • •Mass is neither created nor destroyed
  • •Total mass of reactants = total mass of products
  • •Example: 12 g C + 32 g O2 -> 44 g CO2

Why learn this

It's why every chemical equation must be BALANCED - the foundation of all of chemistry.

💡 Memory trick

Atoms in = atoms out. Nothing vanishes, it just rearranges.