The increasing order of nucleophilicity of the following nucleophiles is a)${\mathrm{CH}}_3{{\mathrm{CO}}_2}^{–}$ b)${\mathrm{H}}_2\mathrm{O}$ c)${\mathrm{CH}}_3{{\mathrm{SO}}_3}^{–}$ d)${\mathrm{OH}}^{–}$

 

Nitrogen is less electronegative than oxygen and will be able to transfer its electrons more readily than oxygen since oxygen  is more electronegative than nitrogen
Nucleophilicity and the likelihood of ion pairs to donate oxygen are decreased. 

Hence the correct answer is A) $\mathrm{b}< \mathrm{c} < \mathrm{a}<\mathrm{d}$