documentclass[twoside,11pt]{exam}

% standard document packages
usepackage[top=0.7in,bottom=0.7in,left=0.36in,right=0.36in]{geometry}
usepackage[T1]{fontenc}
usepackage{baskervald}
usepackage[subscriptcorrection,slantedGreek,nofontinfo,mtpcal,mtpfrak,mtphrb]{mtpro2}
usepackage[english]{babel}

% chemistry packages
usepackage{siunitx}
sisetup{math-rm=ensuremath,inter-unit-product=ensuremath{cdot},per-mode=symbol}

% math packages
usepackage{amsmath}

% exam class settings
renewcommand{choicelabel}{(thechoice)}
renewcommand{choiceshook}{setlength{leftmargin}{18pt}}

begin{document}
    begin{choices}
        choice SI{1.5}{hour}
        CorrectChoice SI{2.5}{hour}
        choice SI{3.5}{hour}
        choice SI{4.0}{hour}
    end{choices}
end{document}

begin{document}
    begin{choices}
        choice SI{1.5}{text{hour}}
        CorrectChoice SI{2.5}{text{hour}}
        choice SI{3.5}{text{hour}}
        choice SI{4.0}{text{hour}}
    end{choices}
end{document}