Common expenses a charge

All sums assessed by the association but unpaid for the share of the common expenses chargeable to any apartment, shall constitute a charge on such apartment, prior to all other charges, except only,-

1. (a) the charge, if any, on the apartment for payment of government and municipal taxes;
2. (b) all sums unpaid on a first mortgage of the apartment;
3. (c) any installment due but unpaid under the hire -purchase agreement; and
4. (d) arrears of ground rent and other charges payable to the lessor.