pBlock ElementsII 1 Question 11
11. The pair in which phosphorus atoms have a formal oxidation state of +3 is
(2016 Main)
(a) pyrophosphorous and hypophosphoric acids
(b) orthophosphorous and hypophosphoric acids
(c) pyrophosphorous and pyrophosphoric acids
(d) orthophosphorous and pyrophosphorous acids
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Solution:
- Orthophosphorous acid, $\mathrm{H}{3} \mathrm{PO}{3}: \mathrm{HO}-{ }_{\mathrm{P}}^{\mathrm{P}}-\mathrm{OH}$
$\mathrm{H}{3} \mathrm{PO}{3}=3+x+3(-2)=0$ or $x=+3$
Pyrophosphorous acid, $\mathrm{H}{4} \mathrm{P}{2} \mathrm{O}_{5}$ :
$\mathrm{H}{4} \stackrel{x}{\mathrm{P}} \mathrm{O}{5}=4+2 x+5(-2)=0$
$4+2 x-10=0, x=+3$
