a,  \({\mathop O\limits^o _2} + 2Mg \to 2Mg\mathop O\limits^{ - 2} \)

b,  \({\mathop {Cl}\limits^o _2} + {H_2}O \mathbin{\lower.3ex\hbox{$\buildrel\textstyle\rightarrow\over
{\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}}$}} H\mathop {Cl}\limits^{ + 1} O + H\mathop {Cl}\limits^{ - 1} \)

c, \(4HF + Si{O_2} \to Si{F_4} + 2{H_2}O\)

d, \({O_3} + 2Ag \to A{g_2}O + {O_2}\)