Hey there!:
Molar mass NaOH = 39.997 g/mol
Number of moles ( solute )
n = mass / molar mass
n = 1.00 / 39.997
n = 0.0250 moles of NaOH
Volume in liters:
500.0 mL / 1000 => 0.5 L
Therefore:
Molarity = number of moles / Volume ( L )
Molarity = 0.0250 / 0.5
Molarity = 0.05 M
Hope that helps!