Base strength of : 
(A) ${\mathrm{H}}_3{\mathrm{CCH}}_2^{-}$ (B) ${\mathrm{H}}_2\mathrm{C}=C{\mathrm{H}}^{-} \mathrm{and}$ (C) $\mathrm{H}-\mathrm{C}\equiv \mathrm{C}¯$is in the order of :

The amount of s-character in various hybrid orbitals is as follows.
$\mathrm{sp}=50\mathrm{\%},{\mathrm{sp}}^2=33\mathrm{\%}\text{ and }{\mathrm{sp}}^3=25\mathrm{\%}$
Therefore s character of the C — H bond in acetylene (sp) is greater than that of the C—H bond in alkene (sp² hybridized) which in turn has greater s character of the C —H bond than in alkanes. Thus owing to a high s character of the C — H bond in alkynes, the electrons constituting this bond are more strongly held by the carbon nucleus with the result the hydrogen present on such a carbon atom can be easily removed as proton. The acidic nature of three types of C— H bonds follows the following order  $-\mathrm{C}\equiv \mathrm{C}-\mathrm{H}>-\mathrm{C}=\mathrm{C}-\mathrm{H}>-\mathrm{C}-\mathrm{C}-\mathrm{H}$ Further, as we know that conjugate base of a strong acid is a weak base, hence the correct order of basicity is $\mathrm{H}-\mathrm{C}\equiv {\mathrm{C}}^{-}<{\mathrm{CH}}_2={\mathrm{CH}}^{-}<{\mathrm{CH}}_3-{\mathrm{CH}}_2^{-}$