The correct order of atomic radii of group 13 elements is

Observe the following oxides. The number of amphoteric oxides from the given list is $\mathrm{CO}, \mathrm{B}_2 \mathrm{O}_3, \mathrm{SnO}_2, \mathrm{PbO}_2, \mathrm{Ga}_2 \mathrm{O}_3, \mathrm{SnO}, \mathrm{PbO}, \mathrm{CO}_2$

Among the following compounds, which one is not primarily responsible for depletion of ozone layer in stratosphere?

Consider the following sequence of reaction. In ' $Z$ ' the number of $s p^3$ carbons is ' $a$ ' and $s p^2$ carbons is ' $b$ '. Value of $(a+b)$ is