There are some deposits of nitrates and phosphates in the earth's crust. Nitrates are more soluble in water. Nitrates are difficult to reduce under laboratory conditions, but microbes do it easily. Ammonia, forms a large number of complexes with transition metals. Hybridization easily explains the ease of sigma donation capability of \(NH_3\) and \(PH_3\).
Phosphine is an inflammable gas, it is prepared from white phosphorus.
Which of the following is the correct statement?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Between nitrates and phosphates, nitrates are less abundant in the earth’s crust.
Nitrogen occurs in the earth’s crust only in small deposits of sodium nitrate (Chile saltpetre) and potassium nitrate (Indian saltpetre); nitrates are very soluble in water, so they are washed away and do not build up. Phosphorus occurs widely in the minerals of the apatite family, which are the main components of phosphate rocks. Phosphorus (about 0.1% of the crust) is far more abundant than nitrogen (about 0.002%), so nitrates are the less abundant of the two.
Why the other options are incorrect
Option (1) Phosphates have no biological significance in humans. — Incorrect. Phosphates are essential in living systems — in bones and teeth (calcium phosphate), in DNA/RNA and in ATP.
Option (2) Between nitrates and phosphates, phosphates are less abundant in the earth’s crust — Incorrect. This reverses the fact; phosphate rocks are far more abundant than nitrate deposits.
Option (4) Oxidation of nitrates is possible in soil. — Incorrect. Nitrogen in the nitrate ion is already in its highest oxidation state (+5), so a nitrate cannot be oxidised further; in soil nitrates are reduced (denitrification), not oxidised.
Note 1: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Occurrence
Note 2: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| – | – | – | 02-06 S3 31-05 S1 | – |