Amongst the given set of reactants, the most appropriate for preparing 2o amine is: 

1.  2o  R - Br + NH3
2.  2oR — Br + NaCN followed by H2/Pt
3.  1o R —NH2 + RCHO followed by H2/Pt
4.  1o R — Br(2 mol) + potassium phthalimide followed by H3O+/ heat

Hint: Nucleophilic addition reaction followed by reduction.

In the first reaction, nucleophilic addition reaction takes place and in the second step reduction reaction takes place.

The chemical transformation is as follows:
While other given set of reactants give primary amine only.