Yellow coloured aqueous solution of sodium chromate changes to orange when acidified with sulphuric acid because:

H^{+}

ions convert chromate ions to dichromate ions

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H^{+}

ions react with sodium chromate to give sodium ions which turn solution orange

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C r^{+}

ions are liberated in the solution which turn the solution orange

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Solution

The correct option is A $H^{+}$ ions convert chromate ions to dichromate ions
The reaction between sodium Chromate and Sulphuric acid is given as:

$2 N a_{2} C r O_{4} + H_{2} S O_{4} \to N a_{2} C r_{2} O_{7} + H_{2} O + N a_{2} S O_{4}$

$C r O_{4}^{2 -}$ (chromate ion) is yellow in colour. When it is acidified by $H^{+}$ in
$C r_{2} O_{7}^{2 -}$ (dichromate ion), the colour changes to orange. Hence option (a) is correct.

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