Here's how to calculate the number of moles in 21.2 g of hydrogen chloride (HCl):

1. Find the molar mass of HCl:

* Hydrogen (H) has a molar mass of approximately 1.01 g/mol.

* Chlorine (Cl) has a molar mass of approximately 35.45 g/mol.

* The molar mass of HCl is 1.01 g/mol + 35.45 g/mol = 36.46 g/mol

2. Use the formula:

* Moles (n) = Mass (m) / Molar Mass (M)

3. Plug in the values:

* n = 21.2 g / 36.46 g/mol

* n ≈ 0.582 moles

Therefore, there are approximately 0.582 moles of hydrogen chloride in 21.2 g.