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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Answer:
Correct Answer: 11. (d)
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, $\mathrm{H} _{4} \mathrm{P} _{2} \mathrm{O} _{5}$ :
$\mathrm{H} _{4} \stackrel{x}{\mathrm{P}} \mathrm{O} _{5}=4+2 x+5(-2)=0$
$4+2 x-10=0, x=+3$
