Question

Assertion : Solution of $Na_2CrO_4$ in water is coloured.
Reason : Oxidation state of $Cr$ in $Na_2CrO_4$ is $+6$.

• A. If both assertion and reason are true and the reason is the correct explanation of the assertion
• B. If both assertion and reason are true and the reason is not the correct explanation of the assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (B)

$Na _{2} CrO _{4}$ solution in water is yellow in colour,

when acidified changes to orange colour (due to the formation of $Cr _{2} O _{2}{ }^{2-}$ ions).

$Na _{2} CrO _{4}+ H _{2} SO _{4} \longrightarrow Na _{2} Cr _{2} O _{7}+ Na _{2} SO _{4}+ H _{2} O$

Oxidation state : $Na _{2} CrO _{4}$

Let oxidation state of $Cr$ be $x$.

$\Rightarrow 2(+1)+x+4(-2)=0 \Rightarrow x=+6$.