Nitrogen & Phosphorus in Agriculture, Environment & Industry – NDA Chemistry PYQs

Solve NDA Chemistry previous-year questions on Nitrogen & Phosphorus with detailed solutions and explanations.

Chapter-wise PYQs • Concept-based explanations • Exam insights

NDA 2026-II

Q. 1. Consider the following statements regarding nitrogen :

I. Nitrogen contains a triple bond.

II. Nitrogen is a triatomic gas.

III. Forces acting between nitrogen molecules are weak van der Waals forces.

Which of the statements given above are correct ?

(a) I and II only

(b) II and III only

(d) I, II and III

Answer: (c) I and III only

Explanation: Statement I: Correct – N₂ contains a triple bond (N≡N). Statement II: Incorrect – nitrogen is a DIATOMIC gas (N₂, two atoms per molecule), not triatomic. Statement III: Correct – between N₂ molecules, only weak van der Waals forces act (N₂ is non-polar). Concept Tested: Properties of N₂ – triple bond, diatomic, van der Waals forces

NDA 2026-I

Q. 2. Superphosphate of lime—a phosphate fertilizer—is obtained by the reaction of

(a) calcium phosphate with sodium hydroxide

(b) calcium phosphate with sulphuric acid

(d) calcium phosphate with nitric acid

Answer: (b) calcium phosphate with sulphuric acid

Explanation: Superphosphate is made by reacting calcium phosphate Ca₃(PO₄)₂ with concentrated sulphuric acid: Ca₃(PO₄)₂ + 2H₂SO₄ → Ca(H₂PO₄)₂ + 2CaSO₄. The product is soluble and more easily absorbed by plants than insoluble calcium phosphate. Concept Tested: Manufacture of superphosphate – Ca₃(PO₄)₂ + H₂SO₄

Q. 3. Which of the following statements is/are correct with regard to Nitrolim?

I. It is prepared by heating calcium carbide with nitrogen.

II. It decomposes into ammonia in soil.

III. It is an NPK fertilizer.

IV. It is an organic fertilizer.

Select the correct answer using the code given below.

(a) I and II only

(b) I, II and III

(d) I, II and IV

Answer: (a) I and II only

Explanation: Nitrolim (calcium cyanamide, CaCN₂) is made by heating calcium carbide (CaC₂) with nitrogen at high temperature – statement I correct. In soil, CaCN₂ hydrolyses to produce ammonia – statement II correct. Nitrolim provides only N, not P and K – it is NOT an NPK fertilizer – statement III wrong. Nitrolim is an inorganic fertilizer – statement IV wrong. Concept Tested: Nitrolim (calcium cyanamide) – preparation and soil action

NDA 2025-I

Q. 4. Which one of the following nitrogen oxides may dimerize?

(a) N₂O

(b) NO₂

(d) N₂O₅

Answer: (b) NO₂

Explanation: NO₂ (nitrogen dioxide) dimerises to form N₂O₄ (dinitrogen tetroxide) at low temperatures or high pressures: 2NO₂ ⇌ N₂O₄. This equilibrium is temperature-dependent – brown NO₂ turns colourless N₂O₄ on cooling. Concept Tested: Dimerisation of NO₂ to N₂O₄

NDA 2024-II

Q. 5. Which one among the following fertilizers is a source of nitrogen?

(a) Superphosphate

(b) Potassium sulfate

(d) Urea

Answer: (d) Urea

Explanation: Urea CO(NH₂)₂ contains ~46.7% nitrogen and is the most widely used nitrogen fertilizer. Superphosphate provides phosphorus. Potassium sulphate provides potassium. Bone meal provides phosphorus. Concept Tested: Nitrogen fertilizer – urea

NDA 2023-I

Q. 6. Which among the following is the popular method for manufacture of ammonia ?

(a) Ostwald’s process

(b) Haber-Bosch process

(d) Electrolysis process

Answer: (b) Haber-Bosch process

Explanation: Ammonia (NH₃) is manufactured industrially by the Haber-Bosch process: N₂ + 3H₂ ⇌ 2NH₃, using an iron catalyst at 400–500 °C and 150–300 atm. Ostwald’s process is used for making nitric acid (from NH₃). Concept Tested: Industrial manufacture of ammonia – Haber-Bosch process

★ JOVIK Exam Insight: Haber process = NH₃ manufacture. Ostwald process = HNO₃ manufacture. NDA tests both.

NDA 2022-I

Q. 7. Which one of the following statements about fertilizers is not correct?

(a) Urea is a phosphorus-containing fertilizer.

(b) Application of fertilizer to the soil increases fertility of the soil.

(d) Urea contains more nitrogen than other fertilizers.

Answer: (a) Urea is a phosphorus-containing fertilizer.

Explanation: Urea (CO(NH₂)₂) contains only C, H, N and O – no phosphorus. It is a nitrogen fertilizer, not a phosphorus fertilizer. Options (b), (c) and (d) are all correct statements about urea and fertilizers. Concept Tested: Urea – nitrogen fertilizer, not phosphorus-containing

NDA 2019-I

Q. 8. Dinitrogen (N₂) and dioxygen (O₂) are the main constituents of air but they do not react with each other to form oxides of nitrogen because

(a) the reaction requires initiation by a catalyst

(b) oxides of nitrogen are unstable

(d) the stoichiometry of N₂ and O₂ in air is not ideal for the reaction to take place

Answer: (c) the reaction is endothermic and requires very high temperature

Explanation: The reaction N₂ + O₂ → 2NO is highly endothermic (ΔH = +180 kJ/mol). It requires very high temperatures (as in lightning or car engines) to proceed. Under normal atmospheric conditions, the temperature is too low for this endothermic reaction to occur spontaneously. Concept Tested: N₂ + O₂ reaction – endothermic, requires high temperature

NDA 2018-II

Q. 9. Which one of the following reactions will give NO (nitric oxide) gas as one of the products?

(a) 3Cu + 8HNO₃ (dilute)→

(b) Cu + 4HNO₃ (conc.)→

(d) Zn + 4HNO₃ (conc.)→

Answer: (a) 3Cu + 8HNO₃ (dilute)→

Explanation: Dilute HNO₃ with copper: 3Cu + 8HNO₃(dilute) → 3Cu(NO₃)₂ + 2NO↑ + 4H₂O. Concentrated HNO₃ with Cu gives NO₂, not NO. Zn with dilute HNO₃ gives N₂O or NH₄⁺, not NO. Concept Tested: Reaction of Cu with dilute HNO₃ – produces NO

★ JOVIK Exam Insight: Dilute HNO₃ → NO. Concentrated HNO₃ → NO₂. This distinction is a common NDA trap.

Q. 10. Which one of the following is not used as fertilizer?

(a) Ammonium nitrate

(b) Ammonium sulphide

(d) Ammonium sulphate

Answer: (b) Ammonium sulphide

Explanation: Ammonium sulphide ((NH₄)₂S) is not used as a fertilizer – it is unstable and smells strongly of H₂S. Ammonium nitrate, ammonium phosphate and ammonium sulphate are all standard nitrogen-containing fertilizers. Concept Tested: Non-fertilizer ammonium compound – ammonium sulphide

NDA 2016-II

Q. 11. Combination of one volume of nitrogen with three volumes of hydrogen produces

(a) one volume of ammonia

(b) two volumes of ammonia

(d) one and a half volumes of ammonia

Answer: (b) two volumes of ammonia

Explanation: N₂ + 3H₂ ⇌ 2NH₃. By Gay-Lussac’s law of combining volumes: 1 vol N₂ + 3 vol H₂ → 2 vol NH₃. The ratio of volumes equals the molar ratio from the balanced equation. Concept Tested: Haber process stoichiometry – N₂:H₂:NH₃ volume ratio

Q. 12. When one strikes a safety match, the first step is

(a) burning of sulfur

(b) decomposition of potassium chlorate into potassium chloride and oxygen

(d) burning of glue and starch

Answer: (c) conversion of a small amount of red phosphorus into white phosphorus

Explanation: When a safety match is struck, friction converts a tiny amount of red phosphorus on the matchbox into highly reactive white phosphorus. This white phosphorus immediately ignites and sets fire to the match head (which contains KClO₃ and other oxidisers). Concept Tested: Safety match ignition – red to white phosphorus conversion

NDA 2016-I

Q. 13. The phosphorus used in the manufacture of safety matches is

(a) Red phosphorus

(b) Black phosphorus

(d) Scarlet phosphorus

Answer: (a) Red phosphorus

Explanation: Safety matches use red phosphorus on the striking surface (matchbox side). White phosphorus is too toxic and dangerously reactive – it was used in old (non-safety) matches. Red phosphorus is much less reactive and safer to use. Concept Tested: Red phosphorus in safety matches

★ JOVIK Exam Insight: Red phosphorus (striking surface) + KClO₃ (match head) = safety match ignition.

Q. 14. Which one of the following oxides of nitrogen is known as ‘anhydride’ of nitric acid ?

(a) N₂O

(b) N₂O₃

(d) N₂O₅

Answer: (d) N₂O₅

Explanation: N₂O₅ (dinitrogen pentoxide) reacts with water to form nitric acid: N₂O₅ + H₂O → 2HNO₃. It is therefore the acid anhydride of nitric acid. N₂O₃ is the anhydride of nitrous acid (HNO₂). Concept Tested: N₂O₅ as anhydride of nitric acid

NDA 2015-II

Q. 15. White Phosphorus glows in the dark due to:

(a) amorphous character

(b) slow oxidation

(d) good conducting property of electricity

Answer: (b) slow oxidation

Explanation: White phosphorus glows in the dark (phosphorescence) because it undergoes slow, continuous oxidation in air, releasing energy as light – a process called chemiluminescence. This is why white phosphorus is stored under water. Concept Tested: Phosphorescence of white phosphorus – slow oxidation

NDA 2015-I

Q. 16. Statement I : Growth of plants is smooth with a complete fertilizer. Statement II : A complete fertilizer always contains N, P, K.

(a) Both the statements are individually true and Statement II is the correct explanation of Statement I

(b) Both the statements are individually true but Statement II is not the correct explanation of Statement I

(d) Statement I is false but Statement II is true

Answer: (a) Both the statements are individually true and Statement II is the correct explanation of Statement I

Explanation: A complete fertilizer is one that contains all three primary plant nutrients: nitrogen (N), phosphorus (P), and potassium (K). Statement I is correct – plants grow better with a balanced NPK fertilizer. Statement II correctly identifies what makes a fertilizer “complete.” II explains I. Concept Tested: Complete fertilizer – NPK composition

Q. 17. Statement I : Colour of nitrogen dioxide changes to colourless at low temperature. Statement II : At low temperature Nitrogen tetroxide (N₂O₄) is formed which is colourless.

(a) Both the statements are individually true and Statement II is the correct explanation of Statement I

(b) Both the statements are individually true but Statement II is not the correct explanation of Statement I

(d) Statement I is false but Statement II is true

Answer: (a) Both the statements are individually true and Statement II is the correct explanation of Statement I

Explanation: NO₂ is a brown/reddish-brown gas. At low temperatures, it dimerises to form N₂O₄ (dinitrogen tetroxide), which is colourless. This explains why the brown colour fades at low temperature. Statement II correctly explains Statement I. Concept Tested: Dimerisation of NO₂ to N₂O₄ at low temperature

Q. 18. Which one among the following is used in making gunpowder ?

(a) Magnesium sulphate

(b) Potassium nitrate

(d) Calcium sulphate

Answer: (b) Potassium nitrate

Explanation: Gunpowder (black powder) is made from a mixture of potassium nitrate (KNO₃), charcoal (carbon), and sulphur. Potassium nitrate is the oxidiser. Sodium stearate is soap. Mg/Ca sulphates are unrelated. Concept Tested: Composition of gunpowder – potassium nitrate as oxidiser

NDA 2014-I

Q. 19. A fertilizer contains 20% nitrogen by mass. To provide a fruit tree with an equivalent of 1 kg of nitrogen, the quantity of fertilizer required is

(a) 20 kg

(b) 0·20 kg

(d) 5 kg

Answer: (d) 5 kg

Explanation: If 20% of the fertilizer is nitrogen: quantity = 1 kg / 0.20 = 5 kg of fertilizer. Concept Tested: Fertilizer calculation – mass required for given nitrogen content

NDA 2013-II

Q. 20. Calcium ammonium nitrate (CAN) is a popular nitrogen fertilizer because it is

(a) slow supplier of nitrogen.

(b) having more percentage of nitrogen in it.

(d) capable of making the soil acidic.

Answer: (a) slow supplier of nitrogen.

Explanation: CAN (calcium ammonium nitrate) is popular because it slowly releases nitrogen, preventing rapid leaching from soil. Calcium also helps buffer soil pH. It is a combined source of ammonium N and nitrate N. Concept Tested: CAN fertilizer – slow nitrogen release

NDA 2012-I

Q. 21. Which one among the following nitrogen compounds has the least percentage of nitrogen by mass?

(a) (NH₄)₃PO₄

(b) NH₃

(d) NH₄NO₃

Answer: (a) (NH₄)₃PO₄

Explanation: Calculate %N: NH₃: 14/17 = 82.4%. NH₄OH: 14/35 = 40%. NH₄NO₃: 28/80 = 35%. (NH₄)₃PO₄: 3×14 = 42 out of 149 = 28.2%. Least %N is in (NH₄)₃PO₄. Concept Tested: Percentage nitrogen by mass – lowest in (NH₄)₃PO₄

NDA 2011-II

Q. 22. During explosion of gunpowder, which of the following gases are evolved in the proportion of 1 : 3 ?

(a) Oxygen : Nitrogen

(b) Nitrogen : Oxygen

(d) Carbon dioxide : Nitrogen

Answer: (c) Nitrogen : Carbon dioxide

Explanation: When gunpowder (KNO₃ + C + S) explodes, the gases produced include N₂ and CO₂ (along with SO₂ and K₂S). The ratio of N₂ to CO₂ in the products is approximately 1:3. Concept Tested: Products of gunpowder explosion – N₂:CO₂ ratio

NDA 2010-I

Q. 23. The metal atom, which is present in superphosphate, is

(a) sodium (Na)

(b) potassium (K)

(d) magnesium (Mg)

Answer: (c) calcium (Ca)

Explanation: Superphosphate of lime is Ca(H₂PO₄)₂, made by reacting calcium phosphate with sulphuric acid. The metal ion is calcium (Ca). It is used as a phosphate fertilizer. Concept Tested: Superphosphate – calcium as the metal component

NDA 2009-I

Q. 24. Which one of the following contains maximum percentage of nitrogen by mass?

(a) Urea

(b) Ammonium cyanide

(d) Ammonium nitrate

Answer: Editorial Review Required

Explanation: Calculate %N: Urea CO(NH₂)₂ = 28/60 = 46.7%. Ammonium cyanide NH₄CN = 28/42 = 66.7%. Ammonium carbonate (NH₄)₂CO₃ = 28/96 = 29.2%. Ammonium nitrate NH₄NO₃ = 28/80 = 35%. On calculation, ammonium cyanide (NH₄CN) has the highest %N at 66.7%, not urea (46.7%). However, urea is commonly listed as the answer in NDA context. Verify official NDA 2009-I key. Concept Tested: Percentage of nitrogen by mass in fertilizer compounds

★ JOVIK Exam Insight: Urea is the most nitrogen-rich common fertilizer (~46.7% N). But ammonium cyanide would have higher %N mathematically. This question needs key verification.