When arsenic sulphide is boiled with $\mathrm{NaOH}$, sodium arsenite and sodium thioarsenite are formed according to reaction:

${\mathrm{xAs}}_2{\mathrm{S}}_3+\mathrm{yNaOH}⟶{\mathrm{xNa}}_3{\mathrm{AsO}}_3+{\mathrm{xNa}}_3{\mathrm{AsS}}_3+\frac{\mathrm{y}}{2}{\mathrm{H}}_2\mathrm{O}$

What are the values of $\mathrm{x}$ and $\mathrm{y}$?

$0.10 \mathrm{g}$ of a sample containing ${\mathrm{CuCO}}_3$ and some inert impurity was dissolved in dilute sulphuric acid and volume made up to $50 \mathrm{mL}.$ This solution was added into $50 \mathrm{mL}$ of $0.04 \mathrm{MKI}$ solution where copper precipitates as $\mathrm{CuI}$ and ${\mathrm{I}}^{-}$is oxidized into ${\mathrm{I}}_3^{-}.$ A $10 \mathrm{mL}$ portion of this solution is taken for analysis, filtered and made up free ${\mathrm{I}}_3^{-}$ and then treated with excess of acidic permanganate solution. Liberated iodine required $20 \mathrm{mL}$ of $2.5 \mathrm{mM}$ sodium thiosulphate solution to reach the end point.

Determine weight percentage of ${\mathrm{CuCO}}_3$ in the original sample,

${\mathrm{HNO}}_3$ oxidizes ${\mathrm{NH}}_4^{+}$ ions to nitrogen and itself gets reduced to ${\mathrm{NO}}_2$. The number of moles of ${\mathrm{HNO}}_3$ required by $1 \mathrm{mol}$ of ${\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4$ is

Assertion: - Law of conservation of mass holds good for nuclear reaction.

Reason:- Law states that mass can be neither created nor destroyed in a chemical reaction.

$300 \mathrm{g}$ of ${\mathrm{CaCO}}_3$ is allowed to react with $294 \mathrm{g}$ of ${\mathrm{H}}_3{\mathrm{PO}}_4$. Calculate : sum of the moles of ${\mathrm{Ca}}_3{\left({\mathrm{PO}}_4\right)}_2$ formed and moles of unreacted reagent.

Molecular mass of CaCO₃ = 100 g/mol

Molecular mass of H₃PO₄ = 98 g/mol