In salt analysis cations of group I and II precipitated in acidic medium and therefore the solution remains acidic till group II. But from III group onwards cations precipitates in basic medium and hence filtrate of group II is to be boiled with con `HNO_(3)` before using it for III group.
The use of `Br_(2)` and NaOH to group III precipitate facilitates

Options

A. rendering Al into sodium meta-aluminate
B. rendering Fe into `Fe(OH)_(2)`
C. conversion of Cr into soluble sodium chromate
D. removal of group III ions before starting group IV

Answer

C

Explanation

`Cr^(3+)` makes soluble sodium chromate in presence of `Br_(2)//NaOH` to allow precipitation.