Match List–I with List–II and select the answer using the code given below the Lists : List–I (Compound) A. Nitrolim B. Ammonium Nitrate C. Urea D. Potassium Nitrate List–II (Chemical Formula) 1. CO(NH2)2 2. KNO3 3. CaNCN 4. NH4NO3 Code :

Correct — B, the code A-3, B-4, C-1, D-2. Take the pairings one at a time. Nitrolim is the fertiliser mixture of calcium cyanamide and carbon, and calcium cyanamide is the compound the paper writes as CaNCN, which is item 3. Ammonium nitrate is NH4NO3, item 4 — the ammonium ion with the nitrate ion, and no other formula in the list contains an ammonium group. Urea is CO(NH2)2, item 1, a carbonyl group carrying two amide nitrogens. Potassium nitrate is KNO3, item 2, which is also saltpetre. That gives 3, 4, 1, 2 in order, and only one code offers it.

• (a)Code A B C D = 1 4 3 2 — Correct for B and D but swaps A and C. It hands urea's formula CO(NH2)2 to Nitrolim and gives urea the cyanamide, which reverses the only two organic-looking entries in the list.
• (c)Code A B C D = 3 2 1 4 — Gets Nitrolim and urea right, then exchanges the two nitrates: ammonium nitrate is given KNO3 and potassium nitrate is given NH4NO3. Reading the metal or the ammonium group at the front of each formula settles this at once.
• (d)Code A B C D = 1 2 3 4 — The straight-through one-to-one code, which matches nothing here except by accident. It gives Nitrolim urea's formula, ammonium nitrate potassium's, urea the cyanamide and potassium nitrate the ammonium salt.

Four nitrogenous compounds and their formulae. Nitrolim is a commercial fertiliser consisting of calcium cyanamide together with carbon; calcium cyanamide is printed in this paper as CaNCN, the form that shows the cyanamide linkage directly, and it is also commonly written CaCN2. In soil it hydrolyses to release ammonia, which is how it feeds a crop. Urea, CO(NH2)2, is the highest-nitrogen solid fertiliser in common use and was the first organic compound made in a laboratory from inorganic starting material. Ammonium nitrate, NH4NO3, and potassium nitrate, KNO3, are both nitrates and both familiar outside agriculture — the first as an industrial explosive component, the second as saltpetre in gunpowder.

A match-list is best walked pairing by pairing rather than by trying to spot the code, because a single confident pairing usually eliminates half the options. Here the two nitrates are the easiest anchor: the formula beginning with NH4 must go to ammonium nitrate and the one beginning with K must go to potassium nitrate, and that alone rules out two codes. Then the remaining choice is only between Nitrolim and urea, and CO(NH2)2 is plainly urea. Read the paper's CaNCN as written; the same compound is often printed as CaCN2 elsewhere, but the pairing is unaffected.

• Nitrolim is calcium cyanamide mixed with carbon; the cyanamide is written CaNCN in this paper.
• Urea is CO(NH2)2 and carries about 46 per cent nitrogen, the highest of the common solid fertilisers.
• Ammonium nitrate is NH4NO3; potassium nitrate is KNO3, also known as saltpetre.
• Calcium cyanamide releases ammonia on hydrolysis in the soil, which is how it acts as a nitrogen fertiliser.
• Wohler's synthesis of urea from ammonium cyanate in 1828 broke the old distinction between organic and inorganic chemistry.

• Guessing a code without walking each pairing — three of the four codes here are right about half the list.
• Confusing ammonium nitrate with potassium nitrate; read the cation at the front of the formula.
• Being thrown by the printed CaNCN — it is calcium cyanamide, the same compound often written CaCN2.

A straightforward formula-recall match, with the codes arranged so that a half-remembered pairing lands on a wrong option.

• practice — not a real PYQ

  Which one of the following fertilisers has the highest percentage of nitrogen?

  • (a)Ammonium sulphate
  • (b)Urea
  • (c)Calcium ammonium nitrate
  • (d)Ammonium nitrate

  Answer(b) Urea — about 46 per cent nitrogen by mass, higher than any other common solid nitrogenous fertiliser.

• practice — not a real PYQ

  Saltpetre, one of the three constituents of traditional gunpowder, is

  • (a)sodium chloride
  • (b)potassium nitrate
  • (c)ammonium nitrate
  • (d)calcium carbonate

  Answer(b) potassium nitrate — KNO3, mixed with charcoal and sulphur in gunpowder.