The glycoalkaloid poison that can build up in green or sprouting potatoes is solanine.
Solanine is a naturally occurring steroidal glycoalkaloid found mainly in potatoes and other nightshades. Potato tubers can accumulate higher concentrations when exposed to light, damaged, stressed or allowed to sprout. Light exposure also causes chlorophyll to form, producing the familiar green color, although the green pigment itself is not the poison.
Symptoms of potato glycoalkaloid poisoning may include a bitter taste, burning in the mouth, nausea, vomiting, abdominal pain, diarrhea and neurological effects. The related compound alpha-chaconine is also important in potatoes, so “solanine” is the standard quiz answer but not the only potato glycoalkaloid of concern.
Cooking does not reliably eliminate these compounds. Removing sprouts and green portions can reduce exposure, but heavily green, bitter or badly sprouted potatoes are best discarded. The other choices are different plant toxins: coniine is associated with poison hemlock, nicotine with tobacco, and atropine with plants such as deadly nightshade.