Match List I with List II and select the correct answer using the code given below the Lists : List I (Chemical process) A. Electrolysis of water B. Burning of coal C. Iron nail immersed in copper sulphate solution D. Addition of barium chloride solution to aluminium sulphate solution List II (Reaction) 1. Double displacement reaction 2. Combination reaction 3. Decomposition reaction 4. Displacement reaction Code :
- (a)A-3 B-4 C-2 D-1
- (b)A-4 B-2 C-1 D-3
- (c)A-3 B-2 C-4 D-1
- (d)A-4 B-1 C-2 D-3
Correct — C, A-3 B-2 C-4 D-1. Write each change as an equation and the type reads off the number of reactants and products. Electrolysis of water is 2H₂O → 2H₂ + O₂, where a single compound breaks down into simpler products, which is a decomposition reaction, so A goes with 3. Burning coal is C + O₂ → CO₂, two substances joining to form one product, which is a combination reaction, so B goes with 2. An iron nail in copper sulphate gives Fe + CuSO₄ → FeSO₄ + Cu, where the more reactive iron pushes copper out of its salt, a displacement reaction, so C goes with 4. Barium chloride added to aluminium sulphate gives 3BaCl₂ + Al₂(SO₄)₃ → 3BaSO₄ + 2AlCl₃, where the ions swap partners and barium sulphate comes down as a precipitate, a double displacement reaction, so D goes with 1.
- (a)A-3 B-4 C-2 D-1 — It gets A and D right but swaps the middle pair, calling the burning of coal a displacement reaction and the iron nail in copper sulphate a combination. Burning coal has carbon and oxygen combining into one product with nothing displaced, and the nail experiment has iron displacing copper from its salt.
- (b)A-4 B-2 C-1 D-3 — It makes the electrolysis of water a displacement reaction, but nothing is displacing anything there — one compound is simply being broken into hydrogen and oxygen. It also calls the nail experiment a double displacement, although only one element changes places and no ions are exchanged.
- (d)A-4 B-1 C-2 D-3 — It repeats the electrolysis error and additionally calls the burning of coal a double displacement reaction, which needs two compounds exchanging ions. Coal burning has an element reacting with a gas, not two compounds swapping partners.
Four basic reaction types cover most school chemistry. A combination reaction has two or more reactants forming a single product. A decomposition reaction has a single reactant breaking into simpler products. A displacement reaction has one element pushing another out of its compound, ordered by the reactivity series. A double displacement reaction has two compounds exchanging ions, and it very often announces itself by throwing down a precipitate.
The fastest route through a match-the-list item like this is elimination rather than working all four out. Only options (a) and (c) begin with A-3, and only one of those pairs the iron nail with displacement, which settles it as (c). If you would rather reason it through, count reactants and products in each equation, then look for a precipitate as the give-away for double displacement. NCERT's own worked case for double displacement is barium chloride with sodium sulphate, which throws down white barium sulphate — the same barium sulphate that forms in entry D here.
- NCERT Class 10 Science defines double displacement reactions as those in which there is an exchange of ions between the reactants, its worked example being barium chloride with sodium sulphate giving a white precipitate of BaSO₄.
- Electrolysis of water splits one compound into two elements, 2H₂O → 2H₂ + O₂, which makes it a decomposition reaction.
- Burning coal is C + O₂ → CO₂, two reactants forming a single product, which makes it a combination reaction.
- An iron nail left in copper sulphate solution gives Fe + CuSO₄ → FeSO₄ + Cu, iron being the more reactive metal and displacing copper.
A-3, B-2, C-4, D-1, which is option (c).
- Calling the burning of coal a decomposition reaction because the coal is consumed — carbon is in fact combining with oxygen.
- Calling electrolysis a displacement reaction because the current seems to drive the gases out; nothing displaces anything, one compound simply breaks up.
- Overlooking that a precipitate is the standard give-away for a double displacement reaction.
NDA gives four everyday chemical changes and asks you to classify them, either as a match-the-list code or as a single which-type item — write the equation first, then count reactants and products and look for a precipitate.
Which one of the following reactions is an example of decomposition reaction?
- (a) CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)
- (b) 2AgCl(s) —Sunlight→ 2Ag(s) + Cl₂(g)
- (c) CuO + H₂ —Heat→ Cu + H₂O
- (d) Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)
Answer(b) 2AgCl(s) —Sunlight→ 2Ag(s) + Cl₂(g)
The single-item version of this match exercise, and its option (d) is the very iron-in-copper-sulphate displacement that entry C tests here.
Which of the following compounds undergoes/undergo thermal decomposition?
- (a) Zinc oxide
- (b) Silver oxide and zinc oxide
- (c) Silver oxide
- (d) Magnesium oxide
Answer(c) Silver oxide
Same decomposition idea in its thermal form, the category that entry A of this match belongs to.
- practice — not a real PYQ
Silver chloride turns grey in sunlight according to 2AgCl → 2Ag + Cl₂. This reaction is an example of
- (a)a combination reaction
- (b)a decomposition reaction
- (c)a displacement reaction
- (d)a double displacement reaction
Answer(b) a decomposition reaction — one compound breaks down into simpler products, here under the action of light.
- practice — not a real PYQ
Adding sodium sulphate solution to barium chloride solution gives a white precipitate of barium sulphate. This reaction is
- (a)a combination reaction
- (b)a displacement reaction
- (c)a double displacement reaction
- (d)a decomposition reaction
Answer(c) a double displacement reaction — the two compounds exchange ions, and the insoluble barium sulphate separates out as a precipitate.