How to box the correct answer in Exam class?

Question

I have tried using the following code:

\documentclass[12pt]{exam}
\CorrectChoiceEmphasis{\mbox{}}
\begin{document}
\begin{questions}
\question Who is an idot? 
\begin{choices}
\choice Not the writer of this post
\CorrectChoiceEmphasis The writter of this post
\end{choices}
\end{questions}
\end{document}

Answer 1

Here are a couple of methods:

• simply using an fbox
• a \tikzmark solution (impossible to resist) based on A \boxed alternative with nicer spacing?.

The code:

\documentclass[12pt]{exam}
\newcommand{\mycorrectchoice}[1]{\CorrectChoice \fbox{#1}}

\usepackage{tikz}
\usetikzlibrary{calc,shapes}

\newcommand{\tikzmark}[1]{\tikz[overlay,remember picture] \node (#1) {};}

\newcommand{\DrawSmartBox}[1][red]{%
    \tikz[overlay,remember picture]{
    \draw[#1]
      ($(bl)+(-1.75em,1em)$) rectangle
      ($(br)+(0.2em,-0.4em)$);}
}

% \MyCorrectSmartChoice:
% #1 optional argument: aspect customization
% #2 mandatory argument: the answer
\newcommand{\MyCorrectSmartChoice}[2][black]{\CorrectChoice \tikzmark{bl}#2\tikzmark{br}\DrawSmartBox[#1]}

\begin{document}
\begin{questions}
\question Who is an idot? 
\begin{choices}
\choice Not the writer of this post
\mycorrectchoice{The writter of this post}
\choice Who read this post
\end{choices}
\question Who is an idot? 
\begin{choices}
\choice Not the writer of this post
\MyCorrectSmartChoice[thick,rounded corners,red]{The writter of this post}
\choice Who read this post
\end{choices}
\end{questions}

\end{document}

The result:

Notice that the example requires two compilation runs because of the \tikzmark macro; furthermore, this approach allows to customize the aspect of the box, as did in the example.