# Most efficient overlapping is

$\begin{array}{1 1}(a)\;sp^2-sp^2& (b)\;s-s \\(c)\;sp^3-sp^3&(d)\;sp-sp\end{array}$

The strength of bonds formed by overlap of $sp^3-sp^3$ bond is more because these orbitals have more directional character.
Hence (b) s-s is the correct answer.
answered Mar 26, 2014