Section 21. Common expenses to be a charge on the apartment

21. Common expenses to be a charge on the apartment.— All sums assessed by the Association of Apartment Owners, 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 — - (i) the charge, if any, on the apartment for payment of Government and municipal taxes; and - (ii) all the sums unpaid on a first mortgage of the apartment.