Sodium reacts with oxygen:

The reaction between sodium and oxygen is a classic example of a metal reacting with a non-metal to form an ionic compound. Sodium is a highly reactive metal, and oxygen is a non-metal that readily reacts with metals to form oxides.

The balanced chemical equation for the reaction between sodium and oxygen is:

2Na + O2 → 2Na2O

Explanation:
- 2Na represents two atoms of sodium.
- O2 represents a molecule of oxygen (which consists of two oxygen atoms).
- 2Na2O represents two units of sodium oxide.

The equation is balanced because the number of atoms on both sides of the equation is equal. On the left-hand side, there are two sodium atoms, and on the right-hand side, there are also two sodium atoms. Similarly, on the left-hand side, there are two oxygen atoms (as O2), and on the right-hand side, there are also two oxygen atoms (as Na2O).

Aluminium reacts with dilute hydrochloric acid:

When aluminium reacts with dilute hydrochloric acid, it undergoes a displacement reaction. Aluminium is a more reactive metal compared to hydrogen, so it displaces hydrogen from hydrochloric acid to form aluminium chloride and hydrogen gas.

The balanced chemical equation for the reaction between aluminium and dilute hydrochloric acid is:

2Al + 6HCl → 2AlCl3 + 3H2

Explanation:
- 2Al represents two atoms of aluminium.
- 6HCl represents six molecules of hydrochloric acid (which consists of one hydrogen atom and one chlorine atom each).
- 2AlCl3 represents two units of aluminium chloride.
- 3H2 represents three molecules of hydrogen gas.

The equation is balanced because the number of atoms on both sides of the equation is equal. On the left-hand side, there are two aluminium atoms and six hydrogen atoms, and on the right-hand side, there are also two aluminium atoms and six hydrogen atoms. Similarly, on the left-hand side, there are six chlorine atoms (as 6HCl), and on the right-hand side, there are also six chlorine atoms (as 2AlCl3).