When characterizing students' item-solving strategies, methods such as interviews and think-aloud protocols are often used. However, these measures provide limited information about sub-or preconscious signals and cognitive processes that also affect students' item-solving strategies and abilities. A growing number of researchers in chemical education research have begun to address this gap by using physiological measurements to assess cognitive load (e.g., heart rate and EEG) and to look at item-solving strategies (e.g., via eye tracking). One physiological measure of cognitive load that has been well-documented in psychology literature is pupil dilation. In this study, two streams of eye-tracking data (gaze and pupillometric data) were combined to reveal information about what mental tasks general chemistry students were engaged in as they answered Chemical Concepts Inventory (CCI) questions (gaze stream) and how those mental tasks elicited changing levels of cognitive load (pupillometric stream). We found that, for complex multiple-choice tasks, pupil dilation fluctuated throughout the course of solving the item. For a more straightforward true/false task, there was a marked difference in pupil signal between participants who correctly answered the question and those who incorrectly answered it. Those who correctly answered the question had linearly increasing pupillary signals, whereas those who incorrectly answered had pupil signals that more closely resembled those observed during the multiple-choice tasks. Interpretations of these differences are supported using retrospective interviews and previously published literature about CCI items.