molarity of a solution means mols per liter.
First, you need to convert 23 grams on NaCl into mols. 23g divided by molar mass (58.44g/mol) which gives you .394 mols.
Now, you need to convert 500ml to L which moves the decimal three places to the left, giving you .500L of solution.
Finally, divide the mols over solution to get .787M
