The option$(s)$ with only amphoteric oxides is(are)
$[A]$ $Cr_2O_3, BeO, SnO, SnO_2$
$[B]$ $Cr_2O_3, CrO, SnO, PbO$
$[C]$ $NO, B_2O_3, PbO, SnO_2$
$[D]$ $ZnO, Al_2O_3, PbO, PbO_2$

Which of the following is a suboxide?

It is observed that $Pb^{2+}$ is more stable than $Pb^{4+}$, while $Sn^{2+}$ is less stable than $Sn^{4+}$. Consider the following reactions:
$PbO_{2} + Pb \rightarrow 2PbO; \Delta_{r}G^{\circ} (1)$
$SnO_{2} + Sn \rightarrow 2SnO; \Delta_{r}G^{\circ} (2)$
Identify the correct set from the following.

Which property of $CO_2$ makes it biologically and geo-chemically important?

Give the chemical reaction for preparing pure $CO$.

How is $H_2S$ liberated in the laboratory?