Which of the following gas readily de-colourises the acidified KMnO$$_4$$ solution?

The oxidation number of Cr in CrO$$_5$$ which has the following structure, is

For decolourisation of 1 mole of KMnO$$_4$$, the moles of H$$_2$$O$$_2$$ required is

In the ionic equation,

$$\mathrm{BiO_3^-+6H^++xe^-\rightarrow Bi^{3+}+3H_2O}$$,

the value of x is