$\begin{array}{1 1} \text{(a)When a silent electric discharge is passed through dry Carbon, ozone is formed.} \\ \text{(b)$2O + O \Rightarrow O_3$} \\ \text{(c) $O_2 + O_2 \Rightarrow O_3$} \\ \text{(d) When a silent electric discharge is passed through dry oxygen, ozone is formed.}\end{array} $
