The pair that on reaction will not evolve $H_2$ gas is  

1.  Copper and HCl (aqueous)
2.  Iron and steam
3.  Iron and $H_{2}S{O}_4$ (aqueous)
4.  Sodium and ethyl alcohol

 $H_2{O}_{\mathrm{2<mspace\; width="1em"></mspace>}}$on oxidation gives:

1. $O^{-2}$

2. $O{H}^{-}$

3. $O_2^{-}$

4. $O_2$

Pure water can be obtained from sea water by:

1.  Centrifugation
2.  Plasmolysis
3.  Reverse osmosis
4.  Sedimentation