Use Mendeléev’s Periodic Table to predict the formulae for the oxides of the following elements:
K, C, AI, Si, Ba.

Explanation

Oxygen is a member of group VIA in Mendeleev's periodic table. Its valency is 2. Similarly, the valencies of all the elements listed can be predicted from their respective groups. This can help in writing the formulae of their oxides.
(i) Potassium (K) is a member of group IA. Its valency is 1. Therefore, the formula of its oxide is `K_(2)O.`
(ii) Carbon (C) is a member of group IVA. Its valency is 4. Therefore, the formula of its oxide is `C_(2)O_(4)" or "CO_(2).`
(iii) Aluminium (Al) belongs to groups IIIA and its valency is 3. The formula of the oxide of the element is `Al_(2)O_(3).`
(iv) Silicon (Si) is present in group IVA after carbon. Its valency is also 4. The formula of its oxide is `Si_(2)O_(4)" or "SiO_(2).` (v) Barium (Ba) belongs to group IIA and the valency of the element is 2. The formula of the oxide of the element is `Ba_(2)O_(2)" or "BaO.`