The decreasing order of acidity is: Acidic strength of any compound is defined as its ability to release H atom as $\mathrm{H}^{+}$ . This atom to which H is attached is highly electronegative. Such atoms tend to pull the bond pair of electrons towards themselves thereby polarising the bond and creating $\delta^{+}$ charge on H. In the compounds in question, the H is attached to carbon atom which does not have a very high electronegativity value. Moreover, the electronegativity of carbon is somewhat increased if the s-character of its hybridised orbitals is high. Greater is the s-character of carbon, greater is its electronegativity as a result of which, the bond pair of electrons of the C – H bond moves towards carbon atom, creating a partial positive charge on H and facilitating its release as $\mathrm{H}^{+}$. Based on this the order of acidic strength may be predicted as

Hybridization of C	sp	$\mathrm{sp}^{2}$	$\mathrm{sp}^{3}$
% s - character	50 %	33 %	25 %