Explain why two oxygen atoms bond to a carbon atom to make a stable molecule of a carbon dioxide?

how many hydrogen atoms are needed to form 5 water molecules

which substances form covalent bonds?

10 H atoms combine with 5 oxygen to form 5 water molecules.

Explanation:

those substances which having low boiling point or low melting point such as water they form covalent bond.

Covalent bonds form between non-metal atoms. Each bond consists of a shared pair of electrons, and is very strong. Simple molecular substances and giant covalent structures have different properties.