$H_3PO_4 + 3OH^{-} \rightarrow PO_4^{3-} + 3H_2O$
${H_2}{O_2}\xrightarrow{{R.T}}{H_2}O + \frac{1}{2}{O_2}$
$\mathrm{Cr}_2 \mathrm{O}_7^{2-}+\mathrm{XH}^{+}+\mathrm{Ye}^{-} \rightarrow 2 \mathrm{~A}+\mathrm{ZH}_2 \mathrm{O}$
$\mathrm{X}, \mathrm{Y}, \mathrm{Z}$ અને $\mathrm{A}$ અનુક્કમે (ક્રમશઃ) શોધો.