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JEE Advanced levelSingle correct optionDifficulty 3 of 3cb017

Phosphorous acid, $H X_{3} PO X_{3}$ , is drawn with one P=O, two P-OH and one P-H bond (P has no lone pair). The total number of lone pairs on all atoms is

A $4$
B $5$
C $6$
D $7$

Answer: C

The P=O oxygen has 2 lone pairs and each of the two OH oxygens has 2 lone pairs, giving

2 + 2 + 2 = 6

. Phosphorus has 5 bonds and no lone pair, and H atoms have none.

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