Among the following elements, $X$ exhibits maximum catenation and $Y$ is the least abundant on earth. $X$ and $Y$ elements are

The oxoacid of phosphorus which contains $4 \mathrm{P}-\mathrm{O}-\mathrm{H}, 2 \mathrm{P}=\mathrm{O}$ and one $\mathrm{P}-\mathrm{O}-\mathrm{P}$ bond is

Group 16 elements are also called

For the reaction, $\mathrm{Br}_2+\mathrm{F}_2$ (excess) ⟶ P , the molecular formula and structure of P , respectively, are