Question $6$: Using the Henderson$-$Hasselbalch equation, calculate the $pH$ of an ammonia buffer when the $N{H}_3$:$N{H}_4^{+}$ratio is $0\mathrm{.}4$ moles:$0\mathrm{.}6$ moles. $)=(9\mathrm{.}25$

$)7\mathrm{.}40$

b$),9\mathrm{.}07$

c$),9\mathrm{.}25$

d$)9\mathrm{.}43$

e$)11\mathrm{.}05$