Which quantity is used to generate the error bars on a graph?
range
median
linear correlation
standard deviation

The error bars on a graph the error or uncertainty of the measure graphed. You can use diffferent statistics to represent this deviation or error, so your graph should state which is being used.

Of the four options listed the only one valid, a frequently used, is the standard deviation (you could use, two standard deviations, or an interval of confidence).

The answer is standard deviation.