JEE Chemistry 2025 Question with Solution

Given: The sequence converts chromyl chloride into a chromate in base and then to dichromate in acid.

Find: The number of terminal oxygen atoms in the final species $C$.

Chromyl chloride $CrO_2Cl_2$ reacts with aqueous $NaOH$ to form chromate, and on acidification chromate gives dichromate.

So, $B = CrO_4^{2-}$ as chromate.

On adding acid:

Thus, $C = Cr_2O_7^{2-}$.

In dichromate ion, two $CrO_4$ tetrahedra share one bridging oxygen $(\mathrm{Cr-O-Cr})$. Therefore, out of $7$ oxygen atoms, $1$ is bridging and the remaining are terminal.

Therefore, the compound $C$ contains $6$ terminal oxygen atoms.

The solution also states that the final species is dichromate and the number of terminal oxygen atoms is $6$.

Given: $CrO_2Cl_2$ is converted to $B$ by base and then to $C$ by acid.

Find: The number of terminal oxygen atoms in $C$.

Use the standard interconversion:

• In base, chromyl chloride gives chromate $CrO_4^{2-}$.
• In acidic medium, chromate condenses to dichromate $Cr_2O_7^{2-}$.

So directly identify $C$ as $Cr_2O_7^{2-}$.

Dichromate has $7$ oxygens total and $1$ bridging oxygen joining the two chromium centers. Hence terminal oxygens are:

Therefore, the required numerical answer is $6$.