Final answer:
Two quantities x and y are proportional if they have the same constant or unit rate. Direct proportionality is represented by y = kx and results in a straight line through the origin on a graph, while inverse proportionality is represented by y = k/x and results in a curve that never intersects the axis.
Step-by-step explanation:
To determine whether two quantities x and y are proportional, we look for a consistent unit rate or constant of proportionality. Two quantities are directly proportional if they increase or decrease by the same rate. This means for every unit change in one variable, there is a predictable and consistent change in the other variable, which can be expressed as y = kx, where k is the constant of proportionality. If you plot this relationship on a graph, it will result in a straight line that passes through the origin (0, 0).
On the other hand, two quantities are inversely proportional if they exhibit a 'more-less' relationship. This means as one variable increases, the other decreases, and it is represented by y = k/x where k is again the constant of proportionality. The graph of inversely proportional variables will be a curve that never intersects the axis.
Thus, the correct answer to the question is B. When two quantities have the same constants/unit rates, they are considered proportional.
An example of direct proportionality in science is when volume is directly proportional to temperature, given that the pressure of the gas is constant.