The weight of a 10 kg mass on Earth, using g = 9.8 m/s², is 98 N. Weight is the gravitational force acting on a mass, calculated with W = mg, so W = 10 kg × 9.8 m/s² = 98 kg·m/s² = 98 N.
The distinction between mass and weight matters here. Mass is an intrinsic property measured in kilograms, while weight is a force measured in newtons. The same 10 kg object keeps its mass on the Moon, but its weight is smaller because lunar gravity is weaker.
The value 9.8 m/s² is a convenient rounded value for Earth’s gravitational acceleration. Standard gravity is defined more precisely as 9.80665 m/s², which would give a weight of 98.0665 N. For ordinary textbook calculations, 98 N is the appropriate rounded result.
People often say that an object “weighs 10 kilograms,” but that is technically describing its mass. A scale may display kilograms because it converts the measured force into an estimated mass using local gravitational conditions.