(b) in the case referred to in sub- clause (ii), so much of the income applied to such purposes in India during the previous year immediately following the previous year in which the income was derived as does not exceed the said amount, may, at the option of the person in receipt of the income (such option to be exercised in writing before the expiry of the time allowed under sub- section (1) 3[ ] of section 139 4[ ] for furnishing the return of income) be deemed to be income applied to such purposes during the previous year in which the income was derived; and the income so deemed to have been applied shall not be taken into account in calculating the amount of income applied to such purposes, in the case referred to in sub- clause (i), during the previous year in which the income is received or during the previous year immediately following, as the case may be, and, in the case referred to in sub- clause (ii), during the previous year immediately following the previous year in which the income was derived.)