Suppose you have an aqueous solution prepared by dissolving $0\mathrm{.}046$mol of $Na{H}_{2}P{O}_4$ in $1L$ of water $)=(7\mathrm{.}21.$ This solution is not a buffer, but suppose you want to make it into one. How many moles of solid $Na{H}_{2}P{O}_4$ must you add to this aqueous solution to make it into:

a$.$ A buffer of $pH7\mathrm{.}21$

$n=,$ mol

b$.$ A buffer of $pH6\mathrm{.}21$

$n=,$mol

c$.$ A buffer of $pH8\mathrm{.}21$

$n=,$ mol