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JEE Advance - Chemistry (2008 - Paper 1 Offline - No. 19)

There are some deposits of nitrates and phosphates in earth's crust. Nitrates are more soluble in water. Nitrates are difficult to reduce under the laboratory conditions but microbes do it easily. Ammonia forms large number of complexes with transition metal ions. Hybridisation easily explains the ease of sigma donation capability of NH$$_3$$ and PH$$_3$$. Phosphine is a flammable gas and is prepared from white phosphorus.
There are some deposits of nitrates and phosphates in earth's crust. Nitrates are more soluble in water. Nitrates are difficult to reduce under the laboratory conditions but microbes do it easily. Ammonia forms large number of complexes with transition metal ions. Hybridisation easily explains the ease of sigma donation capability of NH$$_3$$ and PH$$_3$$. Phosphine is a flammable gas and is prepared from white phosphorus.
There are some deposits of nitrates and phosphates in earth's crust. Nitrates are more soluble in water. Nitrates are difficult to reduce under the laboratory conditions but microbes do it easily. Ammonia forms large number of complexes with transition metal ions. Hybridisation easily explains the ease of sigma donation capability of NH$$_3$$ and PH$$_3$$. Phosphine is a flammable gas and is prepared from white phosphorus.
Among the following, the correct statement is :
Between NH$$_3$$ and PH$$_3$$, NH$$_3$$ is better electron donor because the lone pair of electrons occupies spherical 's' orbital and is less directional.
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.
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.
Between NH$$_3$$ and PH$$_3$$, PH$$_3$$ is better electron donor because the lone pair of electrons occupies spherical 's' orbital and is less directional.

Explanation

Both NH$$_3$$ and PH$$_3$$ have one lone pair of electron on it. The lone pair in case of ammonia occupy sp$$^3$$ orbital is directional.

Hence, the lone pair in case of ammonia is easily available and can be easily donated. But for PH$$_3$$ the lone pair of electrons occupy spherical s-orbital which is less directional and thus its lone pair is not easily available neither it can be donated easily.

Also the lone pair of electrons in sp$$^3$$ orbital has lesser s-character and less attracted by nucleus and available for easy donation than in PH$$_3$$ with pure s orbital, the lone pair in which lone pair are more strongly attracted by nucleus. As we go down a group, the p-character in bond pair increases and the s-character in lone pair increases.

Thus ammonia is a better base than PH$$_3$$.

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