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Which of the following statements about calcium phosphite is INCORRECT?

1. Its molecular formula is Ca3(PO3)2
2. It contains a P–H bond
3. The oxidation state of phosphorus in it is +3
4. All O–P–O bond angles in it are equal

Correct answer: All O–P–O bond angles in it are equal

Solution

Calcium phosphite is Ca(HPO3) or Ca3(HPO3)3 depending on convention; the phosphite ion HPO3²- has the structure where P is bonded to one H, one =O (double bond or dative), and two O⁻ groups. Since one substituent is H (not O), the geometry around P is not symmetric and all O–P–O bond angles are NOT equal. Option D is therefore incorrect. The formula Ca3(PO3)2 (option A) represents the salt of phosphite PO3³-, which is less common, but the oxidation state of P is indeed +3 (option C is correct), and the P–H bond (option B) is correct for H-phosphonate type phosphite.

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