(a)any sum paid by way of contribution towards a recognised provident fund or an approved superannuation fund, subject toββ(i)such limits, as may be prescribed, for recognising the provident fund or approving the superannuation fund; and(ii)such conditions, as the Board may specify, for cases where the contributions are not made annually either as fixed amounts, or annual contributions fixed on some definite basis by reference to the income chargeable under the head "Salaries" or the contributions or to the number of members of the fund;