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

Hydrogen and oxygen combine in the ratio of $1:8$ by mass to form water. What mass of oxygen gas would be required to react completely with $3 \,g$ of hydrogen gas ?

A $0.24\,g$ sample of compound of oxygen and boron was found by analysis to contain $0.096\, g$ of boron and $0.144\, g$ .of oxygen. Calculate the percentage composition of the compound by weight.

What is the mass of –

$(a)$ $1$ mole of nitrogen atoms ?

$(b)$ $4$ moles of aluminium atoms (Atomic mass of aluminium $= 27$ ) ?

$(c)$ $10$ moles of sodium sulphite $(Na_2SO_3)$ ?

When $3.0 \,g$ of carbon is burnt in $8.00 \,g$ oxygen, $11.00 \,g$ of carbon dioxide is produced. What mass of carbon dioxide will be formed when $3.00 \,g$ of carbon is burnt in $50.00\, g$ of oxygen? Which law of chemical combination will govern your answer ?