Question

Number of electron deficient molecules among the following
\(PH_3, B_2H_6, CCl_4, NH_3, LiH \) and \(BCl_3\) is

• A. 0
• B. 1
• C. 2
• D. 3

Answer 1

The Correct Option is C

To determine the number of electron-deficient molecules among the given compounds, we need to understand the concept of electron deficiency. An electron-deficient compound has fewer electrons available for bonding than are required for typical covalent bonding between all of its atoms.

1. \(PH_3\): Phosphine \(PH_3\) is not electron-deficient. It has a full octet around phosphorus, with no deficiency of electrons in bonding.
2. \(B_2H_6\): Diborane \(B_2H_6\) is an electron-deficient compound. Boron, in this compound, forms bonds in a way that involves sharing electrons between more than two atoms (three-center two-electron bonds), indicative of electron deficiency.
3. \(CCl_4\): Carbon tetrachloride \(CCl_4\) is not electron-deficient. The carbon atom achieves a complete octet through single covalent bonds with chlorine atoms.
4. \(NH_3\): Ammonia \(NH_3\) is not electron-deficient. It has a complete octet around the nitrogen atom involving covalent bonds with hydrogen atoms and one lone pair of electrons.
5. \(LiH\): Lithium hydride \(LiH\) is an ionic compound rather than an electron-deficient molecule. Lithium donates an electron to hydrogen, forming a stable ionic bond.
6. \(BCl_3\): Boron trichloride \(BCl_3\) is another electron-deficient compound. Boron has only six electrons in its valence shell after forming three covalent bonds with chlorine, indicating an electron deficiency.

Based on the descriptions above, the electron-deficient molecules are \(B_2H_6\) and \(BCl_3\). Therefore, the number of electron-deficient molecules among the given compounds is 2.