As a part of a medical research study, a researcher exposes two groups of participants to either an actual painkiller or a sugar pill. The participants feel their pain being eliminated even with the sugar pill. In this case, the sugar pill is known as the
placebo

placebo

Explanation:

Based on the information provided within the question it can be said that in this scenario the sugar pill being used is known as a placebo. This term refers to substance or treatment that has no actual effect and has been designed to have no actual therapeutic value other than making individuals think that it does when used. Which in this scenario, not knowing that the pill is a sugar pill and not an actual painkiller, many individuals will still feel the effects that a painkiller pill actually provides even though they did not take one.

how do you know that

explanation:

there are no options provided but you can choose among the following gender-neutral pronouns: zir, hir, eir, vis, tem, eir.

in the normal course of maintaining a pronoun-antecedent agreement, we could have used the words his or her but since we are also required to use gender-neutral language, we need to replace it with its equivalent gender-neutral pronoun.