Question:
Consider the reactions (not balanced)
\[
BF_3 + NaH \xrightarrow{450K} A + NaF
\]
\[
LiH + A \longrightarrow Li^{+}[X]^{-}
\]
The hybridisation involved in $[X]^{-}$ is
Consider the reactions (not balanced)
\[
BF_3 + NaH \xrightarrow{450K} A + NaF
\]
\[
LiH + A \longrightarrow Li^{+}[X]^{-}
\]
The hybridisation involved in $[X]^{-}$ is
Show Hint
Important boron species:
\[
BF_3 \rightarrow B_2H_6 \rightarrow BH_4^-
\]
\[
BH_4^- \text{ is tetrahedral and } sp^3 \text{ hybridised.}
\]
Updated On: Jun 22, 2026
- $sp^2$
- $sp^3$
- $sp$
- $dsp^2$ \bigskip
Show Solution
Verified By Collegedunia
The Correct Option is B
Solution and Explanation
Concept:
Borane chemistry involves formation of borohydride ions through hydride transfer reactions.
Step 1: Identify compound A.
Reaction of boron trifluoride with sodium hydride gives diborane. \[ BF_3 + NaH \rightarrow B_2H_6 + NaF \] Therefore, \[ A = B_2H_6 \]
Step 2: React diborane with lithium hydride.
\[ B_2H_6 + 2LiH \rightarrow 2LiBH_4 \] Hence, \[ [X]^- = BH_4^- \]
Step 3: Determine the geometry of \(BH_4^-\).
Borohydride ion contains four bond pairs around boron. \[ BH_4^- \] Geometry: \[ \text{Tetrahedral} \] Tetrahedral geometry corresponds to \[ sp^3 \] hybridisation. Hence, \[ \boxed{sp^3} \] \[ \boxed{\text{Option (B)}} \]
Step 1: Identify compound A.
Reaction of boron trifluoride with sodium hydride gives diborane. \[ BF_3 + NaH \rightarrow B_2H_6 + NaF \] Therefore, \[ A = B_2H_6 \]
Step 2: React diborane with lithium hydride.
\[ B_2H_6 + 2LiH \rightarrow 2LiBH_4 \] Hence, \[ [X]^- = BH_4^- \]
Step 3: Determine the geometry of \(BH_4^-\).
Borohydride ion contains four bond pairs around boron. \[ BH_4^- \] Geometry: \[ \text{Tetrahedral} \] Tetrahedral geometry corresponds to \[ sp^3 \] hybridisation. Hence, \[ \boxed{sp^3} \] \[ \boxed{\text{Option (B)}} \]
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