(a)[reduce upto fifty percent] [Substituted by Act 5 of 1998 w.e.f. 1.4.1998] in the whole or any part of the [State of Karnataka] [Adapted by the Karnataka Adaptations of Laws Order, 1973 w.e.f. 1.11.1973], if in the opinion of the State Government it is necessary in public interest so to do, the duties with which any particular class of instruments, or any of the instruments belonging to such class, or any instruments when executed by or in favour of any particular class of persons, or by or in favour of any members of such class, are chargeable; and