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

State whether the following statement is true or false:
One atomic mass unit is a mass unit equal to exactly one-twelfth $(1/12)$ the mass of one atom of carbon-$12$.

Express each of the following in kilograms:
$(a)$ $5.84 \times 10^{-3} \,mg$
$(b)$ $58.34 \,g$
$(c)$ $0.584 \,g$
$(d)$ $5.873 \times 10^{-21} \,g$

The unit accepted for measuring the mass of an atom and a molecule is

$(i)$ Name the body which approves the nomenclature of elements and compounds.
$(ii)$ The symbol of sodium is written as $Na$ and not as $S$. Give reason.
$(iii)$ Name one element which forms diatomic and one which forms tetraatomic molecules.

If one mole of carbon atoms weighs $12 \, g$,what is the mass (in grams) of $1$ atom of carbon?