Question

For $Cr{O_3}$ dissolves in aqueous $NaOH$ to give:
$A.$ $CrO_7^{2 - }$
$B.$ $CrO_4^{2 - }$
$C.$ $Cr{\left( {OH} \right)_3}$
$D.$ $Cr{\left( {OH} \right)_2}$

Answer 1

Hint:In the given reaction one reactant is acid and another base so they will give neutralization reaction (A neutralization reaction is the reaction in which acid and base react to produce salt and water).

Complete step by step answer:
We know $Cr{O_3}$ is acidic in nature whereas $NaOH$ is base, when $Cr{O_3}$ is dissolved in aqueous solution it will produce sodium chromate $\left( {N{a_2}Cr{O_4}} \right)$ which is a salt and water. The given reaction below for this process;
$Cr{O_3} + \left( {aq} \right)NaOH \to N{a_2}Cr{O_4} + {H_2}O$
The salt $N{a_2}Cr{O_4}$ is formed when break into ions give rise to $N{a^ + }$ and $CrO_4^{2 - }$ in the solution. Hence, we get $CrO_4^{2 - }$ ion in aqueous solution.
Therefore the correct answer is $B.$

Additional information:
$C{r_2}O_7^{2 - }$ : It is known as dichromate salt containing the dichromate anion. It is oxoanions of chromium in the $ + 6$ oxidation state and is moderately strongest oxidizing agent.
$CrO_4^{2 - }$ : It is known as chromate salt containing the chromate anion. It is also oxoanion of chromium in the $ + 6$ oxidation state and is moderately strongest oxidizing agent. In an aqueous solution both chromate ion and dichromate ions can be interconvertible.
$Cr{\left( {OH} \right)_3}$ : It is known as chromium hydroxide. The color of chromium hydroxide is gelatinous green. The chromium has $ + 3$ oxidation state. It is a polymer with an undefined structure and low solubility. It is amphoteric in nature, that is it can dissolve in both strong alkalis and as well as strong acids.
$N{a_2}Cr{O_4}$ : It is an inorganic salt known as sodium chromate. It is a yellow hygroscopic solid. It is used to make pigment for paints and inks and as a wood preservative and corrosion inhibitor.

Note:
It is to be noted that in a neutralization reaction, there is a combination of ${H^ + }$ and $O{H^ - }$ ions combined to form water. A neutralization reaction is generally an acid-base neutralization reaction.