Step-by-step explanation:
Na:
Na is in group 1. so its oxidation state is 1+. The oxygen in oxides is always 2-. The formula of the sodium oxide is: Na₂O
Since it is a metal, it is a metal oxide and it will produce a sodium hydroxide when reacting with water.
Na₂O + H₂O ---> 2 NaOH
sodium oxide + water ---> sodium hydroxide
The ph of a sodium hydroxide solution is very high.
pH > 7 ---> alkaline
Mg:
Mg is in group 2. so its oxidation state is 2+. The oxygen in oxides is always 2-. The formula of the magnesium oxide is: MgO
Mg is a metal, MgO is a basic oxide and it will produce a magnesium hydroxide when reacting with water.
MgO + H₂O ---> Mg(OH)₂
magnesium oxide + water ---> magnesium hydroxide
The ph of a magnesium hydroxide solution is not as high as sodium hydroxide but it is also very high.
pH > 7 ---> alkaline
Al:
Al is in group 3. so its oxidation state is 3+. The formula of aluminum oxide is: Al₂O₃.
Al₂O₃ is an amphoteric oxide, it can react both with bases and acids. But it is not soluble in water. So it won't react with water. It is practically insoluble because the oxide ions are held with a strong attractive force.
Al₂O₃ + H₂O ---> no reaction
aluminum oxide + water ---> no reaction
pH = 7 ---> neutral
Si:
Si is in group 4. so its oxidation state is 4+. The formula of silicon dioxide is: SiO₂.
Across a period from left to right the electronegativity of atoms increases. We are in group 4, now the electronegativity difference between Si and O is too low to produce an ionic bond. The bond between Si and O is covalent polar.
Silicon dioxide doesn't react with water, because the giant covalent structure is not as reactive (it is difficult to break) as the ionic bonds that we had in sodium oxide or magnesium oxide.
SiO₂ + H₂O ---> no reaction
silicon (IV) oxide + water ---> no reaction
pH = 7 ---> neutral