1. H80 → Hg + 0г 2. Na + Ng → NagN 3. Al + Cl, → AICl 4 MgO + HCI → MgC, + H,0

It seems like you've provided a list of chemical reactions, but some of them contain typographical errors or incorrect symbols. I'll attempt to correct and clarify them for you.

1. H₂O → Hg + O₂
   (Assuming you meant water decomposing into mercury and oxygen, which is not a typical reaction.)

2. Na + Cl₂ → 2NaCl
   (Sodium reacts with chlorine gas to form sodium chloride.)

3. 2Al + 3Cl₂ → 2AlCl₃
   (Aluminum reacts with chlorine gas to form aluminum chloride.)

4. MgO + 2HCl → MgCl₂ + H₂O
   (Magnesium oxide reacts with hydrochloric acid to form magnesium chloride and water.)

If you have specific questions or need further assistance, feel free to ask!