What is the molarity of a hydrochloric acid solution that contains 19.8 g HCl in 100?

How many moles of sodium ions are there in a sample of salt water that contains 4.19?

Molarity is a matter of concentration expressed in moles per dm^3 or moles per litre.

For the first question, 19.8 g of HCl is how many moles? It is 19.8 / (35.5+1) = x moles.

Those x moles is found in 100 cm^3 (I guess, since you didn't put any units)
Find how many moles there are in 1000 cm^3, which is equal to 1 dm^3

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Here again, what is 4.19?

Could you repost your whole question? Topic titles are for titles, and then you type in your question in the bigger box.

I guess here that it is 4.19 M (or mol/dm^3, or mol/L) of NaCl

If there are 4.19 moles in 1 dm^3 of NaCl, find how many there are in the volume of the sample of NaCl.