The correct answer is option 4 - the mass of the body on the Moon would still be 6 kg.
Mass is a measure of the amount of matter in an object, and it does not change based on the gravitational field it is in. In other words, the mass of an object remains constant regardless of its location.
On the Moon, the gravitational pull is about 1/6th of that on Earth. This means that the weight of the object (the force exerted on it due to gravity) would be 1/6th of its weight on Earth. However, mass is different from weight. Weight depends on the strength of the gravitational field, while mass is an inherent property of the object.
So while the weight of the body would change on the Moon (it would be less than on Earth), the mass would remain the same. Therefore, the mass of the body on the Moon would still be 6 kg.
It is important to remember the distinction between mass and weight when considering the effect of gravity on objects. While weight can change depending on the gravitational field, mass remains constant.