A group 15 element forms $\mathrm{d} \pi-\mathrm{d} \pi$ bond with transition metals. It also forms hydride, which is a strongest base among the hydrides of other group members that form $d \pi-d \pi$ bond.

The atomic number of the element is _______ .

Number of oxygen atoms present in chemical formula of fuming sulphuric acid is ___________.

1 mole of $$\mathrm{PbS}$$ is oxidised by "$$\mathrm{X}$$" moles of $$\mathrm{O}_3$$ to get "$$\mathrm{Y}$$" moles of $$\mathrm{O}_2$$. $$\mathrm{X}+\mathrm{Y}=$$ _________.