three column nomenclature coding for the below image

Question

creating three column nomenclature is hard, help me out

Answer 1

Although this is really not a page to let others do your work, I'll help you out. I'm sure you can complete the table yourself. You can also have a look at this question if you dislike my approach.

I'd simply use a standard tabular for this, together with the booktabs package for good-looking tables and the siunitx package for correct typesetting of SI units.

Note that if a subscript is not a mathematical object (index, counter, ...), but has a "normal language meaning" (like "o" for "oxygen", "max" for "maximum", ...) you should set it upright (a_\mathrm{b}).

\documentclass{article}
\usepackage{siunitx,booktabs}
\begin{document}
    \begin{table}[htbp]
        \centering
        \caption{Nomenclature.}
        \label{tab:my_label}
        \begin{tabular}{lll}
            \toprule
            \textbf{Symbol} & \textbf{Description}                       & \textbf{Unit}                    \ \midrule
            $D$             & Diffusion coefficient in the Biofilm phase & \unit{\meter\squared\per\second} \
            $D_o$           & Diffusion coefficient in the Gas phase     & \unit{\meter\squared\per\second} \ 
            \ldots          & \ldots                                     & \ldots                           \ \bottomrule
        \end{tabular}
    \end{table}
\end{document}

Edit

Apparently in newer versions of siunitx one is supposed to use \unit instead of \si (see here), so I changed the code accordingly.