If an object weighs 300 n on earth, what is it’s mass on the moon?

The mass of the object on the Moon (and anywhere else) is about 30.61kg. Please see more detail below.

Explanation:

Weight is the gravitational force exerted on the object and is a function of mass and gravitational acceleration:

(weight) = (mass) x (gravitational acceleration)

We are to find the mass, knowing the weight on Earth to be 300N:

(mass) = (weight on Earth) / (gravitational acceleration on Earth) = 300N / 9.8 m/s^2 = 30.61 kg

The mass of the object is 30.61kg.

The mass of the object is independent of gravity. Therefore the answer to the question "What is its mass on the Moon" is 30.61kg.

If the question were what is its weight on the Moon, the answer would be

(weight on Moon) = (mass) x (grav.accel. on Moon) = 30.61kg x 1.62 m/s^2 = 49.59N

which is about 1/6 of the object's weight on the Earth.