What is the significance of the formula of a substance?

The molecular formula of glucose is${\text{ C}}_6{\text{H}}_{\text{12}}{\text{O}}_6$. Calculate its molecular mass. (Atomic masses: $\text{ C=12 u}$; $\text{H=1 u}$;$\text{ O=16 u}$)

Calculate the molecular mass of the following:

Hydrogen, ${\text{H}}_2$

Calculate the molecular mass of the following :

Oxygen, ${\mathrm{O}}_2$

Calculate the molecular mass of the following:

Chlorine, ${\text{Cl}}_2$

Calculate the molecular mass of the following:

Ammonia,${\text{NH}}_3$

Calculate the molecular mass of the following:

Carbon dioxide, ${\text{CO}}_2$

Calculate the molecular mass of the following compounds:

Methane, ${\mathrm{CH}}_4$