Question

Which of the following conversions involves change in both shape and hybridisation?

• A. $NH _{3} \rightarrow NH _{4}^{+}$
• B. $CH _{4} \rightarrow C _{2} H _{6}$
• C. $H _{2} O \rightarrow H _{3} O ^{+}$
• D. $BF _{3} \rightarrow BF _{4}^{-}$

Answer 1

The Correct Option is D

To determine which conversion involves a change in both shape and hybridization, let's analyze each option:

1. NH_{3} \rightarrow NH_{4}^{+}
   • Hybridization: Ammonia (NH_{3}) is sp^3 hybridized. It forms a tetrahedral geometry, but due to one lone pair, its shape is trigonal pyramidal. For NH_{4}^{+}, the hybridization remains sp^3, and its shape is tetrahedral.
   • Conclusion: The hybridization remains the same but the shape changes from trigonal pyramidal to tetrahedral.
2. CH_{4} \rightarrow C_{2}H_{6}
   • Hybridization: Methane (CH_{4}) is sp^3 hybridized, and ethane (C_{2}H_{6}) is also sp^3 hybridized. Both exhibit a tetrahedral shape around carbon atoms.
   • Conclusion: Neither the hybridization nor the shape changes.
3. H_{2}O \rightarrow H_{3}O^{+}
   • Hybridization: Water (H_{2}O) is sp^3 hybridized with a bent shape. The hydronium ion (H_{3}O^{+}) has the same sp^3 hybridization but the shape changes to trigonal pyramidal.
   • Conclusion: Hybridization remains the same, but the shape changes.
4. BF_{3} \rightarrow BF_{4}^{-}
   • Hybridization: Boron trifluoride (BF_{3}) is sp^2 hybridized and exhibits a trigonal planar shape. The tetrafluoroborate ion (BF_{4}^{-}) is sp^3 hybridized with a tetrahedral shape.
   • Conclusion: Both hybridization changes from sp^2 to sp^3 and the shape changes from trigonal planar to tetrahedral.

Correct Answer Explanation: The conversion BF_{3} \rightarrow BF_{4}^{-} involves a change in both hybridization and shape, making it the correct choice.