Given below are two statements :

Statement I : The first ionization enthalpy of Cr is lower than that of Mn .

Statement II : The second and third ionization enthalpies of Cr are higher than those of Mn .

In the light of the above statements, choose the correct answer from the options given below :

On heating a mixture of common salt and $K_2Cr_2O_7$ in equal amount along with concentrated $H_2SO_4$ in a test tube, a gas is evolved. Formula of the gas evolved and oxidation state of the central metal atom in the gas respectively are:

A. Mn forms the oxide $\mathrm{Mn_2O_7}$, in which Mn is in its highest oxidation state.

B. Oxygen stabilizes the Mn in higher oxidation states by forming multiple bonds with Mn.

C. $\mathrm{Mn_2O_7}$ is an ionic oxide.

D. The structure of $\mathrm{Mn_2O_7}$ consists of one bridged oxygen.

Choose the correct answer from the options given below :

$\mathrm{MnO}_4{ }^{2-}$, in acidic medium, disproportionates to :