In-text Questions — Reactivity of Metals — Metals and Non-metals

1. 12 marksNCERT Cl-10 Science, In-text Qs after §3.2.4, Q1

   Why is sodium kept immersed in kerosene oil?

   Hint. Sodium sits right near the top of the reactivity series — think about what it would meet if left out in the open air.

   Step 1 — Recall how reactive sodium is. Sodium is one of the most reactive metals, reacting vigorously (even violently) with the oxygen and moisture present in ordinary air.

   Step 2 — Explain what kerosene does. Kerosene oil forms a barrier around the sodium, cutting it off from contact with air and moisture, since sodium doesn't react with kerosene itself.

   ✦ Answer: Sodium is kept immersed in kerosene oil because it is so reactive that it would react vigorously (and dangerously) with the oxygen and moisture in air; the kerosene isolates it from the air and prevents this reaction.

   Where students slip. Saying kerosene 'cools' the sodium down — the actual purpose is to physically block air and moisture from reaching it, not to control temperature.

2. 23 marksNCERT Cl-10 Science, In-text Qs after §3.2.4, Q2

   Write equations for the reactions of (i) iron with steam (ii) calcium and potassium with water

   Hint. Iron only reacts with the hotter, more energetic form of water — not cold or even boiling liquid water.

   Step 1 — (i) Iron with steam. Iron doesn't react with cold water, but does react with steam: 3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g).

   Step 2 — (ii) Calcium with water. Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g) — calcium reacts steadily; the bubbles of hydrogen gas cling to its surface, making it float.

   Step 3 — Potassium with water. 2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g) — potassium is far more reactive than calcium, reacting so violently that the reaction is exothermic enough to instantly ignite the hydrogen produced.

   ✦ Answer: (i) 3Fe + 4H₂O → Fe₃O₄ + 4H₂ (ii) Ca + 2H₂O → Ca(OH)₂ + H₂; 2K + 2H₂O → 2KOH + H₂.

   Where students slip. Writing iron's reaction with liquid water instead of steam — iron is not reactive enough to react with cold or boiling liquid water, only with steam.

3. 34 marksNCERT Cl-10 Science, In-text Qs after §3.2.4, Q3

   Samples of four metals A, B, C and D were taken and added to the following solution one by one. The results obtained have been tabulated: A gives no reaction with iron(II) sulphate but displacement with copper(II) sulphate; B gives displacement with iron(II) sulphate but no reaction with zinc sulphate; C gives no reaction with iron(II), copper(II) or zinc sulphate but displacement with silver nitrate; D gives no reaction with all four. (i) Which is the most reactive metal? (ii) What would you observe if B is added to a solution of Copper(II) sulphate? (iii) Arrange the metals A, B, C and D in the order of decreasing reactivity.

   Hint. Chain the individual displacement/no-reaction facts together into one reactivity order before answering any part.

   Step 1 — Turn each result into an inequality. A displaces Cu (A > Cu) but not Fe (A < Fe), so Fe > A > Cu. B displaces Fe (B > Fe) but not Zn (B < Zn), so Zn > B > Fe. C displaces Ag (C > Ag) but not Fe, Cu or Zn (C < all three), so Cu > C > Ag. D reacts with nothing, so D is less reactive than Fe, Cu, Zn and Ag all at once.

   Step 2 — Chain these together. Combining Zn > B > Fe > A > Cu > C > Ag > D gives one consistent order for everything mentioned.

   Step 3 — (i) Most reactive among A, B, C, D. Since B sits above Fe, and everything else in the A/C/D chain sits below Fe, B is the most reactive of the four.

   Step 4 — (ii) B added to copper(II) sulphate. Since B > Fe > A > Cu, B is well above copper in reactivity, so it will displace copper: the blue colour of the copper sulphate solution fades, and reddish-brown copper metal deposits out.

   Step 5 — (iii) Order A, B, C, D by decreasing reactivity. Reading B, A, C, D off the combined chain (B > Fe > A > Cu > C > Ag > D): B > A > C > D.

   ✦ Answer: (i) B is the most reactive. (ii) The blue CuSO₄ solution fades as copper metal is displaced and deposits out. (iii) B > A > C > D.

   Where students slip. Trying to rank A, B, C and D using only the reactions each was directly tested in, without chaining them through the shared reference metals (Fe, Cu, Zn, Ag) — the whole point of the table is that these four reference metals let you compare A, B, C and D indirectly.

4. 42 marksNCERT Cl-10 Science, In-text Qs after §3.2.4, Q4

   Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H₂SO₄.

   Hint. This is the same gas that comes out of every metal-acid reaction in this chapter.

   Step 1 — Name the gas. Hydrogen gas is produced, since a reactive metal displaces hydrogen from a dilute acid.

   Step 2 — Write iron's reaction with dilute sulphuric acid. Fe(s) + H₂SO₄(aq) → FeSO₄(aq) + H₂(g).

   ✦ Answer: Hydrogen gas. Fe + H₂SO₄ → FeSO₄ + H₂.

   Where students slip. Writing FeCl₂ or FeCl₃ as the product — the acid here is sulphuric acid, so the salt formed is iron(II) sulphate, not a chloride.

5. 52 marksNCERT Cl-10 Science, In-text Qs after §3.2.4, Q5

   What would you observe when zinc is added to a solution of iron(II) sulphate? Write the chemical reaction that takes place.

   Hint. Zinc sits above iron in the reactivity series — think about what that means for a displacement reaction here.

   Step 1 — Compare reactivity. Zinc is more reactive than iron, so it can displace iron from iron(II) sulphate solution.

   Step 2 — Write the reaction. Zn(s) + FeSO₄(aq) → ZnSO₄(aq) + Fe(s).

   Step 3 — Describe the observation. The pale green colour of the iron(II) sulphate solution fades (since Fe²⁺ ions are replaced by colourless Zn²⁺ ions), and a grey deposit of iron forms on the zinc.

   ✦ Answer: Zn + FeSO₄ → ZnSO₄ + Fe. The pale green solution fades as it becomes zinc sulphate, and iron metal deposits out.

   Where students slip. Saying the solution turns blue — that would be the copper sulphate case; iron(II) sulphate is pale green, and here that green colour fades as the iron is displaced out.

Solutions written by the tuition.in editorial team and checked against the NCERT Class 10 Science textbook, Reprint 2026-27 (jesc103.pdf) — five in-text question sets (15 questions total, not 18 as some older manifests claim) plus one end-of-chapter Exercise (16 questions, correctly counted). Unchanged by rationalisation.. Questions are referenced from the NCERT textbook for identification.