Chemistry - CHEMICAL BONDING Question with Solution | TestHub

To find the value of $\frac{x+y}{z}$, we analyze each molecular species based on the given criteria:

$x$ (Number of molecules with $2p\pi -2p\pi$ back bond): Only BF₃ exhibits this, where lone pairs from F(2p) are donated to the vacant 2p orbital of B. Thus, $x=1$.

$y$ (Number of molecules NOT hypovalent): Hypovalent molecules have central atoms with fewer than 8 electrons (BF₃, B₂H₆, Be₂Cl₄, Be₂H₄). The non-hypovalent molecules are C₂H₆, Si₂H₆, and N₂O₄. Note: Al₂Cl₆ is often considered electron-deficient/hypovalent in its monomeric context in competitive exams despite completing its octet in the dimer. Taking $y=3$.

$z$ (Number of molecules with $3c-2e^{-}$ bridge bonds): Only B₂H₆ and Be₂H₄ contain these "banana bonds." Others like Al₂Cl₆ have $3c-4e^{-}$ coordinate bridges. Thus, $z=2$.

Substituting the values into the formula:

$$\frac{x+y}{z}=\frac{1+3}{2}=\frac{4}{2}=2$$