# How many hydrogen atoms are in each formula unit of calcium bicarbonate ##Ca(HCO_3)_2##?

two

Looking closely at the part ##(HCO_3)_2##.

In the bracket there is one hydrogen. But outside the bracket, there is a number 2.

It means the number of hydrogen inside the brackets ##xx## 2: [H ##xx## 2] = ##H_2##. Therefore there are two hydrogen atoms present.