The colour imparted by $Co(II)$ compounds to glass is

Which one of the following is an amphoteric oxide?

When $MnO_2$ is fused with $KOH$ in the presence of air,a colored compound is formed. Identify the compound and its color.

$Cr_2O_7^{2-} / H^{\oplus}$ $\xrightarrow[200^{\circ}C]{H_2O_2} 'X'$ $\xrightarrow{\text{On Standing}} 'Y'_{(aq. sol)}$
Select the correct option for $'X'$ and $'Y'$

What is the oxidation state of osmium in $7B$ and $7C$,respectively?

Consider the following reactions:
$NaCl + K_{2}Cr_{2}O_{7} + H_{2}SO_{4}$ (conc.) $\rightarrow (A) +$ side products
$(A) + NaOH \rightarrow (B) +$ side product
$(B) + H_{2}SO_{4}$ (dilute) $+ H_{2}O_{2} \rightarrow (C) +$ side product
The sum of the total number of atoms in one molecule each of $(A)$,$(B)$,and $(C)$ is: