There are #1+4+3xx6# valence electrons to distribute #+1# electrons for the negative charge; thus #24# electrons or #12# electron pairs.
Bonding electrons account for #10# electrons; the remaining #14# electrons are distributed around the oxygen centres, i.e. #7# lone pairs. The formally negative oxygen atom has #3# lone pairs. Of course, this negative charge can be delocalized over the the formally, doubly bound oxygen.