Class 10 Science
17 Practice Questions — The answers are hidden. Reveal them to check your answers. The Timed Test will be available in Phase 3.
Correct option: B — Combination reaction
Combination (or synthesis) joins reactants into one product, e.g. C + O₂ → CO₂.
Correct option: C — Thermal decomposition
Heat splits lead nitrate into oxide, nitrogen dioxide and oxygen — thermal decomposition.
Correct option: B — Displacement
More reactive zinc displaces copper from CuSO₄. It is also a redox change.
Correct option: B — Oxidised
Magnesium gains oxygen (and loses electrons) so it is oxidised.
Correct option: B — Because mass is conserved in a chemical change
Atoms are rearranged, not created or destroyed — atom counts on both sides must match.
Correct option: D — Double displacement (precipitation)
Ions exchange partners and BaSO₄ comes out as a precipitate.
Correct option: B — Oxidation of iron in moist air
Iron combines with oxygen (and moisture) to form hydrated iron oxide — oxidation.
Correct option: B — 2H₂ + O₂ → 2H₂O
Two H₂ molecules need one O₂ to make two water molecules.
A decomposition reaction splits one compound into two or more products. Example: heating limestone CaCO₃ → CaO + CO₂, or electrolysis of water.
Look for heat, light or electricity as the energy that breaks the reactant.
A redox reaction has oxidation and reduction together. Copper is oxidised (gains oxygen); oxygen is reduced.
If a metal gains oxygen, that metal is oxidised.
Law of conservation of mass: mass (and number of each atom) on the reactant side equals the product side.
Never change formulae — only change coefficients.
1) Combination: A + B → AB, e.g. 2H₂ + O₂ → 2H₂O.
2) Decomposition: AB → A + B, e.g. 2HgO → 2Hg + O₂.
3) Displacement: A + BC → AC + B, e.g. Zn + CuSO₄ → ZnSO₄ + Cu.
4) Double displacement: AB + CD → AD + CB, e.g. AgNO₃ + NaCl → AgCl↓ + NaNO₃.
Many of these can also be redox if electrons are transferred.
Board answers score better when each type has a labelled equation.
Oxidation: gain of oxygen / loss of hydrogen / loss of electrons.
Reduction: loss of oxygen / gain of hydrogen / gain of electrons.
In 2H₂S + SO₂ → 3S + 2H₂O, H₂S loses hydrogen (oxidised) and SO₂ loses oxygen (reduced). Electrons move from sulphur in H₂S toward sulphur in SO₂.
Name the oxidising agent (the one that gets reduced) in the last line.
Correct option: B — An acid
Acids turn blue litmus red; bases turn red litmus blue.
Correct option: B — 7
pH 7 is neutral at 25 °C; below 7 acidic, above 7 basic.
If mouth pH falls below about 5.5, enamel (calcium phosphate) starts dissolving. Bacteria produce acid from sugar, so rinsing and cleaning keeps pH safer.
Link sugar → acid → low pH → enamel damage.
Acids produce H⁺ (or H₃O⁺) in water, taste sour, turn blue litmus red — e.g. lemon juice / HCl.
Bases produce OH⁻, feel soapy, turn red litmus blue — e.g. soap solution / NaOH.
They neutralise each other to give salt and water.
Mention one strong and one weak example if the question has marks for that.
These practice sets use original GKSchools wording — they are not a verbatim dump of the NCERT textbook. “Important” means high-weight practice for the chapter, not a claim that these are previous-year exam questions.
