Here it is
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Mix up of C...H and O....H acidity.
I would say none of these  has right order.
COOH > CH

I would say 3>4>2>1

The least acidic is the last one because in that there is no resonance of the conjugate base.
However in I,II and III there is strong conjugation of the conjugate base.
Now more stronger delocalization due to more electron withdrawing group, there will be more stabilization  of conjugate base and more stronger is the acid.
EWG -NO2 strongest>-CN>-ester
Accordingly decide the acidity trend.
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