$Cl_2O_7$ is the anhydride of $HClO_4$. It reacts with water slowly to give perchloric acid $Cl_2O_7 + H_2 O \to \underset{\text{Perchlororic acid}}{2HClO_4}$ Its structure is as follows
It is less reactive than other oxides of chlorine and does not react with $P, S$, coal or paper at room temperature.
P block elements are those in which the last electron enters any of the three p-orbitals of their respective shells. Since a p-subshell has three degenerate p-orbitals each of which can accommodate two electrons, therefore in all there are six groups of p-block elements.
P block elements are shiny and usually a good conductor of electricity and heat as they have a tendency to lose an electron. You will find some amazing properties of elements in a P-block element like gallium. It’s a metal that can melt in the palm of your hand. Silicon is also one of the most important metalloids of the p-block group as it is an important component of glass.
