Element showing the phenomenon of allotropy is

Consider the oxides of group $14$ elements $SiO_2$,$GeO_2$,$SnO_2$,$PbO_2$,$CO$ and $GeO$. The amphoteric oxides are

The element whose hydride contains the maximum number of hydrogen atoms per atom of the element is

Discuss the reactivity of group $14$ elements towards water and halogens.

In which of the following is the inert pair effect most prominent?

Reaction of $NaCl$ with conc. $H_2SO_4$ liberates a gas,$X$ that turns moist blue litmus paper red. When gas $X$ is passed into a test tube containing egg shell powder suspended in water,another gas,$Y$ is generated which when passed through lime water makes it milky. The gases $X$ and $Y$,respectively,are