The words "Alleviate", "Mitigate", and "Assuage" all refer to reducing or easing something, while "Exacerbate" refers to making a situation worse. Therefore, "Exacerbate" is the odd one out.
\begin{itemize}
\item Option (b) Alleviate: This word means to ease or make a situation less severe, which is opposite to "Exacerbate".
\item Option (c) Mitigate: Similar to "Alleviate", "Mitigate" means to make less severe or harsh.
\item Option (d) Assuage: It means to soothe or lessen the intensity of something, which is opposite of "Exacerbate".
\end{itemize}