Match List–I with List–II and select the answer using the code given below the Lists : List–I (Reaction) A. CH4 + 2O2 → CO2 + 2H2O + heat and light B. Mg + H2SO4 → MgSO4 + H2 C. 2NaOH + H2SO4 → Na2SO4 + 2H2O D. NaCl + AgNO3 → NaNO3 + AgCl List–II (Type of Reaction) 1. Combustion 2. Double displacement 3. Displacement 4. Neutralization Code :

Correct — A, the code A-1, B-3, C-4, D-2. Take the reactions one at a time. Methane burning in oxygen to carbon dioxide and water with heat and light is combustion, item 1 — the phrase 'heat and light' in the equation is the giveaway. Magnesium with sulphuric acid giving magnesium sulphate and hydrogen is displacement, item 3, because the more reactive metal has pushed hydrogen out of the acid. Sodium hydroxide with sulphuric acid giving sodium sulphate and water is neutralisation, item 4, an acid and a base giving a salt and water. Sodium chloride with silver nitrate giving sodium nitrate and silver chloride is double displacement, item 2, since the two compounds have exchanged their ions.

• (b)Code A B C D = 1 4 3 2 — Right about combustion and double displacement but swaps the middle pair, calling the magnesium reaction a neutralisation and the alkali-acid reaction a displacement. An acid meeting a base gives a salt and water, which is neutralisation by definition; a metal pushing out hydrogen is displacement.
• (c)Code A B C D = 2 3 4 1 — Correct for B and C but exchanges combustion with double displacement. Methane burning is not an ion exchange, and silver chloride precipitating from two solutions releases no light.
• (d)Code A B C D = 2 4 3 1 — Wrong at every position. It calls the methane combustion a double displacement, the magnesium displacement a neutralisation, the acid-base reaction a displacement and the precipitation a combustion.

School chemistry sorts reactions into a small number of named types. Combination joins two substances into one; decomposition splits one into several; displacement has a more reactive element pushing a less reactive one out of its compound; double displacement has two compounds exchanging partners, often producing a precipitate; neutralisation is the particular double-displacement case of an acid and a base giving a salt and water; and combustion is rapid reaction with oxygen releasing heat and usually light. A single reaction can carry more than one label, which is why a match-list must be read for the best fit rather than the only fit.

The overlap between the categories is the real difficulty here. Neutralisation is technically a kind of double displacement, so a candidate who spots the ion exchange in reaction C may pair it with item 2 and then be forced into an error at D. The resolution is that the list offers a more specific label for C, and a more specific label always wins in a match-list. Work the two unambiguous reactions first — the methane combustion and the magnesium displacement — and the remaining two follow.

• Combustion is rapid reaction with oxygen accompanied by heat and light.
• A displacement reaction has a more reactive element replacing a less reactive one in its compound.
• In double displacement two compounds exchange ions, frequently giving a precipitate.
• Neutralisation is acid plus base giving salt and water, and is a special case of double displacement.
• Silver chloride is a white insoluble precipitate, which is why the sodium chloride and silver nitrate reaction is used as a test for chloride.

• Labelling the acid-base reaction as double displacement when neutralisation is offered.
• Missing that 'heat and light' in the written equation is the examiner's marker for combustion.
• Guessing a code from one confident pairing; here three of the four codes get at least one position right.

A reaction-type match in which two categories genuinely overlap, so the item rewards choosing the most specific available label.

• practice — not a real PYQ

  The reaction between sodium chloride solution and silver nitrate solution, which gives a white precipitate, is an example of

  • (a)combination
  • (b)displacement
  • (c)double displacement
  • (d)decomposition

  Answer(c) double displacement — the two compounds exchange ions and insoluble silver chloride separates out.

• practice — not a real PYQ

  Zinc added to dilute hydrochloric acid liberates hydrogen gas. This reaction is best classified as

  • (a)a displacement reaction
  • (b)a double displacement reaction
  • (c)a combination reaction
  • (d)a neutralisation reaction

  Answer(a) a displacement reaction — zinc is above hydrogen in the reactivity series and pushes it out of the acid.