The amount of arsenic pentasulphide that can be obtained when 35 ....

$2{H}_{3}As{O}_{4} + 5{H}_{2}S\overset{Conc . HCl}{\to}A{s}_{2}{S}_{5} + 8{H}_{2}O$

$2$ moles of Arsenic Acid $\to$ $1$ mole of Arsenic Pentasulphide

$1$ moles of Arsenic Acid $\to$ $1 / 2$ mole of Arsenic Pentasulphide

Molarmassof{H}_{3}As{O}_{4} = 141; MolarmassofA{s}_{2}{S}_{5} = 308$<br /><br />$∴$Number of moles of${H}_{3}As{O}_{4} = \dfrac{35.5}{141} = 0.25$<br /><br />$∴$Number of moles of$A{s}_{2}{S}_{5} = \dfrac{0.25}{2} = 0.125mol