When borax is heated with cobalt oxide,which of the following compounds produces a blue-colored bead?

$I$. $4FeCr_2O_4 + 16NaOH + 7O_2 \rightarrow 8Na_2CrO_4 + 2Fe_2O_3 + 8H_2O$ (where $A = Na_2CrO_4$)
$II$. $2Na_2CrO_4 + H_2SO_4 \rightarrow Na_2Cr_2O_7 + Na_2SO_4 + H_2O$ (where $B = H_2SO_4$)
Compounds $(A)$ and $(B)$ are :

$A$ group of acidic oxides is

Given below are two statements:
Statement $I :$ Potassium permanganate on heating at $573 \ K$ forms potassium manganate.
Statement $II :$ Both potassium permanganate and potassium manganate are tetrahedral and paramagnetic in nature.
In the light of the above statements,choose the most appropriate answer from the options given below.

Provide the structures of the following ions:
$1.$ $CrO_4^{2-}$
$2.$ $Cr_2O_7^{2-}$

Which one of the following statements is correct when $SO_2$ is passed through acidified $K_2Cr_2O_7$ solution?