Final answer:
An object's weight would be greatest on Earth, as weight is determined by the local force of gravity, and Earth has the highest acceleration due to gravity among the mentioned bodies.
Step-by-step explanation:
An object's weight would be the greatest on Earth compared to its weight on Pluto, Mercury, or the Moon. Weight is a measure of the force of gravity on an object, which is directly proportional to the acceleration due to gravity at a given location. Since Earth has a higher acceleration due to gravity (≈ 9.80 m/s²) than the Moon (≈ 1.67 m/s²), Mercury, or Pluto, the object would weigh more on Earth. Remember that an object's mass remains constant while its weight varies with gravity.