Hydrides

Diborane reacts with metal hydrides in diethyl ether to give metal borohydrides.
Example: So, X must be a metal hydride such as , etc.

In this question, we are tasked with identifying the correct pair of hydrides. Let’s analyze each option: 1. Electron deficient hydrides are typically formed by elements that do not have a full octet of electrons, such as , which does not fit this definition. Hence, this is not the correct answer. 2. Saline hydrides are those formed with alkali and alkaline earth metals, not , so option (2) is incorrect. 3. Electron precise hydrides are those where the central atom has a complete octet. , however, doesn't qualify as electron precise, hence this pair is incorrect. 4. Electron rich hydrides such as are correct because nitrogen has a lone pair of electrons that make it electron-rich. Thus, the correct answer is option (4).

- Saline hydrides are known to react quickly with water, not slowly. Hence, option (1) is incorrect.
- Group 14 elements (e.g., Si, Ge, Sn, Pb) form electron-precise hydrides, making option (2) correct.
- BaCl .2H O involves water of crystallization, not hydrogen-bonded water. Hence, option (3) is incorrect.
- The density of ice is less than that of water, not more, making option (4) incorrect.

- Electron-deficient hydrides: typically group 13 elements like B and Al (e.g., B H )
- Electron-rich hydrides: group 15 elements like N and P with lone pairs (e.g., NH )
- Electron-precise hydrides: group 14 elements (e.g., CH , SiH )
- Interstitial hydrides: transition metals (e.g., TiH , Group 4)

Hydrides are categorized as:
- Saline (Ionic): Formed by alkali/alkaline earth metals (e.g., NaH)
- Electron-rich: Contain lone pairs (e.g., H₂O)
- Electron-deficient: Lack sufficient electrons for bonding (e.g., B₂H₆)
- Electron-precise: Have exact electrons required for bonding (e.g., CH₄, NH₃)
HF contains a lone pair on fluorine, making it electron-rich, not electron-precise.

Let’s evaluate each: - I. : Produces - II. : Lewis acid-base reaction, no - III. - IV. : Forms , no Only I and III produce hydrogen gas.