Calculate the number of hydrogen atoms in 2 moles of HCl.

We know that 1 mole of HCl = 6.023 x 10²³ molecules of HCl

So, 2 moles of HCl = 2 x 6.023 x 10²³ molecules of HCl

= 12.046 x 10²³ molecules of HCl

Now,

1 molecule of HCl = 1 hydrogen atom

Therefore, 

12.046 x 10²³ molecules of HCl = 12.046 x 10²³ hydrogen atoms.