Among the following compounds, strongest acid is

In ethane $\left(C_2{H}_6\right)$  and benzene $\left(C_6{H}_6\right)$  hydrogen atoms are present on $s{p}^3$  and $s{p}^2$ hybridised carbon atom, so these are very weak acids as compared to $CH\equiv CH$ (having $sp$ carbon) and $C{H}_{3}OH$ (having electronegative oxygen) To decide whether $CH\equiv CH$  or $C{H}_{3}OH$  is a stronger acid, consider the following reaction.

$HC\equiv C^{-}N{a}^{+}+\underset{\left(strongeracid\right)}{C{H}_{3}OH}\to \underset{\left(wea\ker acid\right)}{HC}\equiv CH+C{H}_3{O}^{-}N{a}^{+}$  

Since a stronger acid displaces a weaker acid from its salts, therefore, $C{H}_{3}OH$ is a stronger acid than$HC\equiv CH$ . Alternatively, $C{H}_3{O}^{-}$  is weaker base than $HC\equiv C^{-}$  because oxygen can accommodate negative charge easily.