Which one of the following is not correct?

a$.$Calcination is the removal of chemically bound $H_{2}O$

b$.$When $ZnS$ is completely roasted to ZnO, it is called dead roasting

c$.S{O}_2$ and $S{O}_4$ form during roasting of sulfides.

d$.$Formation of $S_2$ does not have an adverse effect for roasting of sulfides