How is sodium chromate converted into sodium dichromate in the manufacture of potassium dichromate from chromite ore?

Which of the following statements is incorrect?

Silver halides are used in photography because:

Which compounds are formed when $Mn_2O_7$ and $CrO_3$ react with water,given that they are acidic in nature?

Given below are two statements:
Statement $I$: Fusion of $MnO_2$ with $KOH$ and an oxidising agent gives dark green $K_2MnO_4$.
Statement $II$: Manganate ion on electrolytic oxidation in alkaline medium gives permanganate ion.
In the light of the above statements,choose the correct answer from the options given below.

The transition element of $III-B$ group which forms an alum isomorphic with $Al_2(SO_4)_3 \cdot 18H_2O$ is $Sc$. The color of the compound $Sc_2(SO_4)_3 \cdot (NH_4)_2SO_4 \cdot 24H_2O$ is: