1. Calculate the molar mass of HCl:

* Hydrogen (H) has a molar mass of 1.008 g/mol.

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

* Molar mass of HCl = 1.008 g/mol + 35.45 g/mol = 36.458 g/mol

2. Convert grams of HCl to moles:

* Moles = (mass in grams) / (molar mass)

* Moles of HCl = 0.340 g / 36.458 g/mol = 0.00933 mol

3. Use Avogadro's number to find the number of molecules:

* Avogadro's number states that 1 mole of any substance contains 6.022 x 10^23 molecules.

* Number of HCl molecules = (moles of HCl) * (Avogadro's number)

* Number of HCl molecules = 0.00933 mol * 6.022 x 10^23 molecules/mol

* Number of HCl molecules ≈ 5.62 x 10^21 molecules

Therefore, there are approximately 5.62 x 10^21 HCl molecules present in 0.340 g of HCl.