d-block Questions

Acidified ${\text{K}}_2{\text{Cr}}_2{\text{O}}_7$ solution turns green when ${\text{Na}}_2{\text{SO}}_3$ is added to it. This is due to the formation of:

For the four successive transition elements ($\text{Cr, Mn, Fe}$ and $\text{Co}$), the stability of $+2$ oxidation state will be there in which of the following order? (At. nos. $\text{Cr}=24,\text{Mn}=25,\text{Fe}=26,\text{Co}=27$)

An aqueous solution of ${\text{CoCl}}_2$ on addition of excess of concentrated $\text{HCl}$ turns blue due to formation of:

Among the following pairs of ions, the lower oxidation state in aqueous solution is more stable than the other, in:

Which one of the following ions is the most stable in aqueous solution? (At. No. $\text{Ti}=22,\text{V}=23,\text{Cr}=24,\text{Mn}=25$)

Which of the statements is NOT true?

Which of the following statements about interstitial compounds is incorrect?

The reaction of aqueous ${\text{KMnO}}_4$ with ${\text{H}}_2{\text{O}}_2$ in acidic conditions gives: