What is the molarity of a solution which contains 58.5 g of sodium chloride dissolved in 0.500 l of solution?

The units of molarity are moles/liter, so you want to find the number of moles in one liter of a substance.
The molar mass of Sodium Chloride (NaCl) is approximately 58.5, gotten from the sum of the molar masses of sodium and chlorine
Molar Mass sodium = 23.0 grams/mole
Molar Mass chlorine = 35.5 grams/mole
Molar mass sodium chloride = 23.0 g/mol + 35.5 g/mol = 58.5 g/mol
Convert 58.5 grams to moles: (58.5 grams)/(58.5 grams/mol)
Leaves 1.00 moles of NaCl
Divide that by the number of liters of solution (0.500 liters)
(1.00moles)/(0.500 liters) = 2.00 moles/liter is your molarity