The treatment of an aqueous solution of 3 . 74g of Cu ( NO _ 3 ) _...

Number of moles of $Cu{\left({NO}_{3}\right)}_{2} = \dfrac{3 . 74}{187} = 0 . 02$

$2Cu{\left({NO}_{3}\right)}_{2} + 4KI \to {Cu}_{2}{I}_{2} ↓ + {I}_{2} + 4{KNO}_{3}$

Number of moles of ${Cu}_{2}{l}_{2}$ precipitated $= 0 . 01$

${I}_{2}\left(brownsolution\right) + {H}_{2}S \to S ↓ + 2HI$

Number of moles of $S$ precipitated $= 0 . 01$

Mass of $S$ precipitates $= \left(0 . 01 \times 32\right)g = 0 . 32g$