PLEASE HELP...STUCK WITH THIS PORTION?

NaCl and KOH are ionic compounds for which "formula units" should be used instead of "molecules".
Avogadro constant = 6.02 × 10²³ /mol

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- Calculate the number of molecules in 20 g sample of NaCl?

Molar mass of NaCl = (23.0 + 35.5) g/mol = 58.5 g/mol
No. of moles of NaCl = (20 g) / (58.5 g/mol) = 0.3419 mol
No. of NaCl molecules = (0.3419 mol) × (6.02 × 10²³ molecules/mol) = 2.06 × 10²³ molecules

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- Calculate the number of molecules in 40 g sample of KOH?

Molar mass of KOH = (39.0 + 16.0 + 1.0) g/mol = 56.0 g/mol
No. of moles of KOH = (40 g) / (56.0 g/mol) = 0.7143 mol
No. of KOH molecules = (0.7143 mol) × (6.02 × 10²³ molecules/mol) = 4.3 × 10²³ molecules

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- Calculate the number of molecules in 50 g sample of H₂O?

Molar mass of H₂O = (1.0×2 + 16.0) g/mol = 18.0 g/mol
No. of moles of H₂O = (50 g) / (18.0 g/mol) = 2.778 mol
No. of H₂O molecules = (2.778 mol) × (6.02 × 10²³ molecules/mol) = 1.67 × 10²⁴ molecules

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- Calculate the number of molecules in 25 g sample of HCl?

Molar mass of HCl = (1.0 + 35.5) g/mol = 36.5 g/mol
No. of moles of HCl = (25 g) / (36.5 g/mol) = 0.6849 mol
No. of HCl molecules = (0.6849 mol) × (6.02 × 10²³ molecules/mol) = 4.12 × 10²³ molecules

To calculate the number of molecules, you will first have to convert to moles. Since you are given the mass of the sample, we can convert to moles, using molar mass. Next, once we've obtain our mole value, we use Avogadro's Number (6.022*10^23) which is the number of molecules in a mole. I'll do the first one.

20g * (1molNaCl/58.44g) * ((6.022*10^23molecules)/ 1mol NaCl) = 2.061*10^23 molecules

It might be helpful if you keep track of units because it helps guide you to an answer.
Good luck!