To determine the constant of proportionality in this context, we start by noting that the recipe requires 2 cups of flour for each loaf of bread. The constant of proportionality can be determined as the ratio of the amount of flour (in cups) to the number of loaves of bread.
Given that the recipe calls for 2 cups of flour per loaf, the constant of proportionality \( k \) is:
\[ k = \frac{\text{cups of flour}}{\text{number of loaves}} = \frac{2 \text{ cups}}{1 \text{ loaf}} = 2 \]
Thus, the constant of proportionality appears as the ratio of flour to loaves, which can be expressed as \( (2, 1) \) because for every 2 cups of flour (the y-coordinate), there is 1 loaf of bread (the x-coordinate).
Therefore, the ordered pair that represents the constant of proportionality is:
\[ (2, 1) \]