Assertion: Dilute $H X_{2} SO X_{4}$ liberates $CO X_{2}$ from the cold solid of both a carbonate and a hydrogencarbonate. Reason: A cold solution of $MgSO X_{4}$ gives an immediate white precipitate with $CO X_{3} X^{2 -}$ but not with $HCO X_{3} X^{-}$ .

ABoth the assertion and the reason are true, and the reason explains the assertion
BBoth the assertion and the reason are true, but the reason does not explain the assertion
CThe assertion is true but the reason is false
DThe assertion is false but the reason is true

Answer: B

Both

CO X_{3} X^{2 -}

and

HCO X_{3} X^{-}

react with dilute acid to give effervescence of

CO X_{2}

, so the assertion is true. The reason is also a true fact:

MgCO X_{3}

precipitates in the cold while

Mg (HCO X_{3}) X_{2}

is soluble. However, the MgSO4 behaviour is not why acid liberates

CO X_{2}

, so the reason does not explain the assertion.