# How many hydrogen atoms are present in the compound C_6H_12O_6?

The subscript (small numbers after the element symbol) tells you how many atoms of the element are in one molecule of the compound. So, ${H}_{12}$ indicates that there are 12 atoms of Hydrogen in that one molecule of ${C}_{6} {H}_{12} {O}_{6}$.
Fun fact: ${C}_{6} {H}_{12} {O}_{6}$ is more commonly known as glucose, a simple sugar.