I want to maintain readability of each element by using alignment point. At the same time I also don't want to make any further confusion as shown in the following figure in which the closing curly brace is not properly placed.

documentclass[preview,border=12pt,varwidth]{standalone}

usepackage{mathtools}

begin{document}

abovedisplayskip=0pt

[A ={

    begin{aligned}[t]

         &R_1R_1,R_1R_2,R_1P_1,R_1P_2,R_1P_3,\

         &R_2R_1,R_2R_2,R_2P_1,R_2P_2,R_2P_3

    end{aligned}

}]

end{document}

Question

How to move the closing curly brace to the proper place as shown in red? Any other suggestion is always welcome.

You can instead use the {...} environment inside the aligned environment

documentclass[preview,border=12pt,varwidth]{standalone}

usepackage{amsmath}

begin{document}

abovedisplayskip=0pt



    [begin{aligned}[t]

         A={&R_1R_1,R_1R_2,R_1P_1,R_1P_2,R_1P_3,\

         &R_2R_1,R_2R_2,R_2P_1,R_2P_2,R_2P_3}

    end{aligned}]

end{document}

to get:

Here are two suggestions, one a multlined the other a large brace:

documentclass{article}



usepackage{mathtools}



begin{document}

begin{equation*}

  A =

    begin{multlined}[t]

         {R_1R_1,R_1R_2,R_1P_1,R_1P_2,R_1P_3,\

         R_2R_1,R_2R_2,R_2P_1,R_2P_2,R_2P_3}

    end{multlined}

end{equation*}



begin{equation*}

  A =biggl{

    begin{aligned}

         &R_1R_1,R_1R_2,R_1P_1,R_1P_2,R_1P_3,\

         &R_2R_1,R_2R_2,R_2P_1,R_2P_2,R_2P_3

    end{aligned}

biggr}

end{equation*}



end{document}

Inspired by Raaja's answer.

documentclass[preview,border=12pt,varwidth]{standalone}

usepackage{mathtools}

usepackage[a6paper]{geometry}

begin{document}

abovedisplayskip=0pt

[

begin{split}

        A ={ &R_1R_1,R_1R_2,R_1P_1,R_1P_2,R_1P_3,\

                    &R_2R_1,R_2R_2,R_2P_1,R_2P_2,R_2P_3}

end{split}

]

end{document}

Note: usepackage[a6paper]{geometry} is added because varwidth does not take any effect if split is used.