Correct statements from the following are

A. Potassium dichromate is an oxidising agent and it oxidises $\mathrm{FeSO}_4$ to $\mathrm{Fe}_2\left(\mathrm{SO}_4\right)_3$ in acidic medium.

B. Sodium dichromate can be used as primary standard in volumetric estimation.

C. $\mathrm{CrO}_4^{2-}$ and $\mathrm{Cr}_2 \mathrm{O}_7^{2-}$ are interconvertible in aqueous solution by varying the pH of the solution.

D. $\mathrm{Cr}-\mathrm{O}-\mathrm{Cr}$ bond angle in $\mathrm{Cr}_2 \mathrm{O}_7^{2-}$ is $126^{\circ}$.

Choose the correct answer from the options given below :

Among $Fe^{2+}$, $Fe^{3+}$, $Cr^{2+}$ and $Zn^{2+}$, the ion that shows positive borax bead test and with highest ionisation enthalpy is :

Which of the following sets includes all the species that will change the orange colour of $\mathrm{K_2Cr_2O_7}$ in acidic medium?

Consider the following statements about manganate and permanganate ions. Identify the correct statements.

A. The geometry of both manganate and permanganate ions is tetrahedral.

B. The oxidation states of Mn in manganate and permanganate are +7 and +6, respectively.

C. Oxidation of Mn(II) salt by peroxodisulphate gives manganate ion as the final product.

D. Manganate ion is paramagnetic and permanganate ion is diamagnetic.

E. Acidified permanganate ion reduces oxalate, nitrite and iodide ions.

Choose the correct answer from the options given below :