(c)where it relates to an assessee to which sub-section (1) applies,––(i)only that amount which exceeds the credit balance in the provision for bad and doubtful debts account made under that sub-section shall be allowed as deduction;(ii)such amount shall be allowed only when the assessee has debited any amount of bad debt or part thereof in that tax year to the provision for bad and doubtful debts account made under that sub-section; and(iii)the aforesaid account shall be only one such account under sub-section (1) and such account shall be related to all types of advances, including advances made by rural branches.