(c)any instrument chargeable [with a duty not exceeding fifteen naye paise] [Substituted by Act 29 of 1962 w.e.f. 1.10.1962] or a mortgage of crop [Article [35] [Substituted by Act 29 of 1962 w.e.f. 1.10.1962](a) of the Schedule] chargeable under clause (a) or (b) of section 3 with a duty of twenty-five naye paise, when brought to him, after the execution thereof, on paper not duly stamped.