If the strength of gravity is 9.8 newtons per kilogram, that means:

a. each newton of force equals 9.8 pounds.
b. each pound of force equals 9.8 newtons.
c. each newton of mass weighs 9.8 kilograms
d. each kilogram of mass weighs 9.8 newtons

To determine the correct answer, we need to understand the relationship between force, mass, and weight. The strength of gravity is typically measured as an acceleration, which means it is given in units of meters per second squared (m/s²). However, in this case, it is stated as 9.8 newtons per kilogram (N/kg), which can be interpreted as the gravitational force acting on a mass.

Using this information, let's examine each option:

a. Each newton of force equals 9.8 pounds: This is incorrect because pounds is a unit of force in the English system, whereas newtons are the metric unit of force. The conversion between pounds and newtons is not 9.8.

b. Each pound of force equals 9.8 newtons: This is also incorrect because, as mentioned before, pounds and newtons are different units of force. The conversion between these units is not 9.8.

c. Each newton of mass weighs 9.8 kilograms: This is incorrect because mass is not equal to weight. Mass is a property of an object that measures the amount of matter in it and is measured in kilograms (kg). Weight, on the other hand, is the force exerted on an object due to gravity and is measured in newtons (N). The given information states the gravitational strength (9.8 N/kg), which implies the force exerted by gravity on each kilogram of mass, not the mass itself.

d. Each kilogram of mass weighs 9.8 newtons: This is the correct answer. When we say that the strength of gravity is 9.8 newtons per kilogram, it means that each kilogram of mass experiences a gravitational force of 9.8 newtons. Weight can be calculated by multiplying the mass by the gravitational strength (F = m * g), where F is the force in newtons, m is the mass in kilograms, and g is the gravitational strength in N/kg (9.8 N/kg in this case).

Therefore, the correct answer is: d. each kilogram of mass weighs 9.8 newtons.

d. each kilogram of mass weighs 9.8 newtons