Determine the conjugate base of each species.
Part 1 of 3
For \( \mathrm{H}_{3} \mathrm{PO}_{4} \), the conjugate base is \( \square \) .
Part 2 of 3
For \( \mathrm{H}_{2} \mathrm{O} \), the conjugate base is \( \square \) .
Part 3 of 3
For \( \mathrm{HCN} \), the conjugate base is \( \square \) .