Why is it not possible to see an atom with naked eyes?

Which postulate of Dalton's atomic theory can explain the law of definite proportions?

Define the atomic mass unit.

Write down the formulae of:

(i) Sodium oxide

(ii) Aluminum chloride

(iii) Sodium sulphide

(iv) Magnesium hydroxide

Write down the names of compounds represented by the following formulae:

(i) Al₂(S0₄)₃

(ii) CaCl₂

(iii) K₂S0₄

(iv) KN0₃

(v) CaC0₃