Assertion :When $N a_{2} C O_{3}$ is titrated against $H C l$ in presence of phenolphthalein indicator, it is converted to $N a C l$ . Reason: Phenolphthalein shows color change in the $p H$ range of $3.5 - 4.6$ .

Choose the correct option.

Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

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Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion

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Assertion is correct but Reason is incorrect

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Assertion is incorrect but Reason is correct

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Solution

The correct option is C Assertion is correct but Reason is incorrect
When $N a_{2} C O_{3}$ reacts with HCl, the compound is neutralized in a step-wise manner, that is, $N a H C O_{3}$ is formed first before they are completely transformed to $H_{2} C O_{3}$ (or $C O_{2} + H_{2} O$ ).

$N a_{2} C O_{3} + H C l \to N a H C O_{3} + N a C l$ ..........(I)

$N a H C O_{3} + H C l \to H_{2} C O_{3} + N a C l$ ............(II)
In the presence of Phenolphthalein (phph) indicator, it only shows the
(I) reaction. Phenolphthalein shows the colour change at pH 8.2 to 10.
Hence, the Assertion is correct but Reason is incorrect.
Option C.

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