The earth exerts a gravitational force of 0.500 n on an object. what is the mass of the object in g?

Gravitational force (weight) = (mass) times (acceleration of gravity).

On or near the surface of the Earth, the acceleration of gravity is
about 9.8 m/s².

Within that region . . .      (0.5 newton) = (mass) x (9.8 m/s²)

Divide each side by 9.8m/s²:      Mass = (0.5 newton) / (9.8 m/s²)

                                                   Mass  =  0.051 kilogram = 51 grams
                                                                                             (rounded)