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: 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 — 2H₂ + O₂ → 2H₂O
Two H₂ molecules need one O₂ to make two water molecules.
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.
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.
