Answer the question on the basis of the passage given below:
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 of \(NH_3\) and \(PH_3\).
Phosphine is an inflammable gas, it is prepared from white phosphorus.
Among the following the correct statement is
A. Between \(NH_3\) and \(PH_3\), \(NH_3\) is a better electron donor because the lone pair of electrons occupy spherical 's' orbital and is less directional.
B. Between \(NH_3\) and \(PH_3\), \(NH_3\) is a better electron donor because the lone pair of electrons occupies '\(sp^3\)' orbital and is more directional.
C. Between \(NH_3\) and \(PH_3\), \(PH_3\) is a better electron donor because the lone pair of electrons occupies '\(sp^3\)' orbital and is more directional.
D. Between \(NH_3\) and \(PH_3\), \(PH_3\) is a better electron donor because the lone pair of electrons occupy spherical 's' orbital and is less directional.
Choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → B only
A molecule is a good electron-pair donor when its lone pair is concentrated and directional. In \( \ce{NH3} \) nitrogen is sp3 hybridised, and the lone pair sits in an sp3 orbital that points away from the atom. In \( \ce{PH3} \) the bonds are formed almost with pure p orbitals (bond angle about 93.6°), and the lone pair stays in an almost pure, spherical 3s orbital, which is non-directional and spread over a large atom. So \( \ce{NH3} \) is the better electron donor.
(A) Between NH3 and PH3, NH3 is a better electron donor because the lone pair of electrons occupy spherical ‘s’ orbital and is less directional. — False. In \( \ce{NH3} \) the lone pair is in an sp3 orbital, not a spherical s orbital.
(B) Between NH3 and PH3, NH3 is a better electron donor because the lone pair of electrons occupies ‘sp3’ orbital and is more directional. — True. Both the comparison and the reason are right: the directional sp3 lone pair of N is easily donated.
(C) Between NH3 and PH3, PH3 is a better electron donor because the lone pair of electrons occupies ‘sp3’ orbital and is more directional. — False. \( \ce{PH3} \) is the poorer donor, and its lone pair is not in an sp3 orbital.
(D) Between NH3 and PH3, PH3 is a better electron donor because the lone pair of electrons occupy spherical ‘s’ orbital and is less directional. — False. The lone pair of \( \ce{PH3} \) is in a spherical s orbital, but that makes \( \ce{PH3} \) a poorer donor, not a better one.
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.
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 | – |