Which ion gives a violet-coloured bead in the borax bead test?

The compound called microcosmic salt is

Assign $A, B, C, D$ from the given type of reaction.
$MCrO_4 \downarrow (M^{2+} = Ba^{2+}, Pb^{2+}) + AcOH \longrightarrow$ No dissolution

What is the formula of microcosmic salt?

In the flame test of a mixture of salts,a green flame with a blue centre was observed. Which one of the following cations may be present?

Which of the following solid salt on heating with solid $K_2Cr_2O_7$ and conc. $H_2SO_4$ evolves orange-red vapours that turn an aqueous $NaOH$ solution yellow?