B. To enable the e-governance
egov works fine even without a single identity. You need one per department.
and have totally unnecessary duplication of systems and data..
not only will it be costlier, it will also give very little value addition, if some department for industries cannot cross reference your records from other department (law, taxes, whatever)
also let us see how practical that is, total number of central government departments == a few hundred avg. number of state government departments == a few hundred (multiply this by number of states)
having separate identity per department is like the old 1990's systems in big companies before LDAP.. ie, u had a separate login to each system.. today all major corporations are moving towards single sign-on for different intra company systems.