Answer:
0.491 mol NaCl
Step-by-step explanation:
Convert from grams to moles using the molar mass of NaCl:
28.7 g NaCl x 1 mol NaCl/58.44 g NaCl = 0.491 mol NaCl
The molar mass (58.44 g) can be found from adding the molar masses of the individual elements (Na and Cl); the g NaCl will cancel out (dimensional analysis), leaving you with mol NaCl.