The number of moles of NH _ 3 , that must be added to 2L of 0 . 80...

Let no. moles of ${NH}_{3}$ added $= x$

${Ag}^{+} ( aq ) + 2{NH}_{3} ( aq ) ⇌ {\left[Ag{\left({NH}_{3}\right)}_{2}\right]}^{+} ( aq )$

$t = 0 0 . 8 \dfrac{x}{2}$

$t = \infty 5 \times {10}^{- 8} \left(\dfrac{x}{2} - 1 . 6\right) 0 . 8$

${K}_{eq} = \dfrac{\left[{\left[Ag{\left({NH}_{3}\right)}_{2}\right]}^{+}\right]}{\left[{Ag}^{+}\right]{\left[{NH}_{3}\right]}^{2}}$

$\dfrac{x}{2} - 1 . 6 = 0 . 4$

$x = 4$