Final answer:
The quantity that will produce a straight line when plotted against time in the context of Bismuth's radioactive decay is Concentration vs. Time.
Step-by-step explanation:
The question is asking which quantity will produce a straight line when plotted against time in the context of Bismuth undergoing radioactive decay. From the options given, the answer is A. Concentration vs. Time. When a radioactive substance undergoes decay, its concentration decreases over time. Plotting the concentration of the radioactive substance against time will result in a straight line, as shown in Figure 19.2.1.