because the standard deviation describes how far, on average, each observation is from the typical value. a bigger variance means observations are more distant from the typical value, and therefore, more dispersed
is positive for all values of and . As pointed out, , so for all . This means the proportion of occupied binding sites is an increasing function of the concentration of oxygen, meaning the presence of more oxygen is consistent with greater availability of binding sites. (The question says as much in the second sentence.)