Reason
One H-atom is non-ionizable in more stable tautomeric form of $$H_{3}PO_{3}.$$
Assertion
In $$H_{3}PO_{3},$$ basicity of the oxy acid is two.
A
Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B
Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
C
Assertion is correct but Reason is incorrect
D
Both Assertion and Reason are incorrect
Correct option is A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
In more stable structure (B) one H-atom is non-ionizable hence its basicity is $$2$$.
Hence, Option "A" is the correct answer.