When $KMn{O_4}$ reacts with $B{r_2}$ in a weak alkaline medium gives bromate ion. Then oxidation state of $Mn$ changes from $ + 7$ to:
1) $ + 6$
2)$ + 4$
3) $ + 3$
4) $ + 2$

Hint: We know that the oxidation state, at times alluded to as oxidation number, depicts the level of oxidation (loss of electrons) of a molecule in a synthetic compound. Adroitly, the oxidation state, which might be positive, negative or zero, is the theoretical charge that an iota would have if all bonds to particles of various components were \[100\% \] ionic, with no covalent segment. This is never precisely valid for genuine bonds.

Complete answer:
$2Mn{O_4}^ - + B{r^ - } + {H_2}O\xrightarrow{{}}2Mn{O_2} + Br{O_3}^ - + 2O{H^ - }$
Let us calculate the oxidation of manganese in $Mn{O_2}$,
$x + 2\left( { - 2} \right) = 0$
$ \Rightarrow x = + 4$
Thus the oxidation state changes from $ + 7$ to $ + 4$.

Hence option 2 is correct.

Additional information:
Potassium permanganate is an inorganic compound with the synthetic equation \[KMn{O_4}\] and made out of \[{K^ + }\] and \[Mn{O_4} - \]. It is a purplish-dark glasslike salt that disintegrates in water to give seriously pink or purple arrangements. Potassium permanganate is broadly utilized in the compound industry and labs as a solid oxidizing specialist, and furthermore as a drug for dermatitis, for cleaning wounds, and general sterilization.

Note:
As we know that potassium permanganate can be utilized to quantitatively decide the absolute oxidizable natural material in a fluid example. The worth decided is known as the permanganate esteem. In logical science, a normalized fluid arrangement of \[KMn{O_4}\] is now and again utilized as an oxidizing titrant for redox titrations (permanganometry). As potassium permanganate is titrated, the arrangement turns into a light shade of red, which obscures as overabundance of the titrant is added to the arrangement. In a connected manner, it is utilized as a reagent to decide the Kappa number of wood mash. For the normalization of \[KMn{O_4}\] arrangements, decrease by oxalic corrosive is frequently used. Watery, acidic arrangements of \[KMn{O_4}\] are utilized to gather vaporous mercury in pipe gas during fixed source emanations testing.