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I am trying to put a tabularx inside a tcolorbox but it's not centered properly, it's shifted slightly to the right. Here is the code I am using. I am using figure environment for the caption. Is there a better way to do this?

documentclass[12pt, a4paper]{article}

usepackage[top=1in, bottom=1.5in, right=1in, left=1in]{geometry}

usepackage{tabularx}

usepackage{tcolorbox}

usepackage{chemfig}



newcolumntype{Y}{>{centeringarraybackslash}X}



begin{document}



begin{figure}[ht]

centering

begin{tcolorbox}

begin{tabularx}{1linewidth}{YYYY}

{}chemfig{C(-[:90,.6]H)(-[:180,.6]H)(-[:270,.6]H) -[,.6]C(-[:90,.6]H)(-[:0,.6]H)(-[:270,.6]H)} &

{}chemfig{C(-[:135,.6]H)(-[:225,.6]H) =[,.6]C(-[:45,.6]H)(-[:315,.6]H)}                        &

{}chemfig{C(-[:135,.6]H)(-[:225,.6]H) =[,.6]C=[,.6]C(-[:45,.6]H)(-[:315,.6]H)}                 &

{}chemfig{C(-[:180,.6]H) ~[,.6]C -[,.6]C(-[:90,.6]H)(-[:0,.6]H)(-[:270,.6]H)}                  \[5ex]



(a) Ethane & (b) Ethylene & (c) Propadiene & (d) Propyne\

end{tabularx}



end{tcolorbox} 

    vspace{-1.5ex}

caption{caption}

    label{fig:my_label}

end{figure}



end{document}

Since line breaking inside the cells is neither expected nor desirable, and since the natural widths of the four columns are quite different, using a tabularx environment seems wrong. I suggest you use a tabular* environment instead.

documentclass[12pt, a4paper]{article}

usepackage[top=1in, bottom=1.5in, hmargin=1in]{geometry}

usepackage{tcolorbox,chemfig}



begin{document}



begin{figure}[ht]

setlengthtabcolsep{0pt} % let LaTeX figure out intercolumn spacing

begin{tcolorbox}

begin{tabular*}{1linewidth}{@{extracolsep{fill}} cccc }

chemfig{C(-[:90,.6]H)(-[:180,.6]H)(-[:270,.6]H) -[,.6]C(-[:90,.6]H)(-[:0,.6]H)(-[:270,.6]H)} &

chemfig{C(-[:135,.6]H)(-[:225,.6]H) =[,.6]C(-[:45,.6]H)(-[:315,.6]H)}                        &

chemfig{C(-[:135,.6]H)(-[:225,.6]H) =[,.6]C=[,.6]C(-[:45,.6]H)(-[:315,.6]H)}                 &

chemfig{C(-[:180,.6]H) ~[,.6]C -[,.6]C(-[:90,.6]H)(-[:0,.6]H)(-[:270,.6]H)}  \[5ex]

(a) Ethane & (b) Ethylene & (c) Propadiene & (d) Propyne\

end{tabular*}

end{tcolorbox}

vspace{-2ex}

caption{caption}

label{fig:my_label}

end{figure}



end{document}