Resizing a table to fit the page

Question

\begin{table}
\centering
\begin{center}
\begin{tabular}{p{1.25in}ddd}
\toprule
\multicolumn{1}{C{0.2in}}{Degree} & \multicolumn{1}{C{1.5in}}{$H^*(K(\Z_2,n+1);\Z_2)$} & \multicolumn{1}{C{1.5in}}{$H^*(K(\Z,n);\Z_2)$}\\
\midrule
n &  & \iota_n \\
n+1 & \iota_{n+1} \tikzmark{a1} &  \\
n+2 & \Sq^1\iota_{n+1} \tikzmark{a2} & \tikzmark{b1} \Sq^2\iota_n \\
&&\\
n+3 & \Sq^2\iota_{n+1} & \tikzmark{b2} \Sq^3\iota_n \\
 & \Sq^2\Sq^1\iota_{n+1} & \\
&&\\
n+4 & \Sq^3\iota_{n+1} & \Sq^4\iota_n \\
 & \Sq^2\Sq^1\iota_{n+1} \tikzmark{a3} & \\
&&\\
n+5 & \Sq^4\iota_{n+1} \tikzmark{a4} & \tikzmark{b3} \Sq^5\iota_n \\
 & \Sq^3\Sq^1\iota_{n+1} & \\
&&\\
n+6 & \Sq^5\iota_{n+1} \tikzmark{a5} & \Sq^6\iota_{n+1} \\
 & \Sq^4\Sq^1\iota_{n+1} \tikzmark{a6} & \tikzmark{b4} \Sq^4\Sq^2\iota_n \\
&&\\
n+7 & \Sq^6\iota_{n+1} \tikzmark{a7} & \Sq^7\iota_n \\
 & \Sq^5\Sq^1\iota_{n+1} & \tikzmark{b5} \Sq^5\Sq^2\iota_n \\
 & \Sq4\Sq^2\iota_{n+1} & \\
&&\\
n+8 & \Sq^7\iota_{n+1} \tikzmark{a8} & \Sq^8\iota_n \\
 & \Sq^6\Sq^1\iota_{n+1} \tikzmark{a9} & \tikzmark{b6} \Sq^6\Sq^2\iota_n \\
 & \Sq^5\Sq^2\iota_{n+1} & \\
 & \Sq^4\Sq^2\Sq^1\iota_{n+1} \tikzmark{a10} & \\
&&\\
n+9 & \Sq^8\iota_{n+1} \tikzmark{a11} & \tikzmark{b7} \Sq^9\iota_n \\
 & \Sq^7\Sq^1\iota_{n+1} \tikzmark{a12} & \tikzmark{b8} \Sq^7\Sq^2\iota_n \\
 & \Sq^6\Sq^2\iota_{n+1} & \tikzmark{b9} \Sq^6\Sq^3\iota_n \\
 & \Sq^5\Sq^2\Sq^1\iota_{n+1} & \\
&&\\
n+10 & \Sq^{9}\iota_{n+1} & \Sq^{10}\iota_n \\
 & \Sq^8\Sq^1\iota_{n+1} & \tikzmark{b10} \Sq^8\Sq^2\iota_n \\
 & \Sq^7\Sq^2\iota_{n+1} & \tikzmark{b11} \Sq^7\Sq^3\iota_n \\
 & \Sq^6\Sq^3\iota_{n+1} & \\
 & \Sq^6\Sq^2\Sq^1\iota_{n+1} & \\
\bottomrule
\end{tabular}

\begin{tikzpicture}[overlay, remember picture, yshift=.1\baselineskip, xshift=.1, shorten >=5pt, shorten <=0pt]
   \draw [->] ([yshift=0pt, xshift=5pt]{pic cs:a1}) -- ({pic cs:b1});
   \draw [->] ([yshift=0pt, xshift=5pt]{pic cs:a2}) -- ({pic cs:b2});
   \draw [->] ([yshift=0pt, xshift=5pt]{pic cs:a3}) -- ({pic cs:b3});
   \draw [->] ([yshift=0pt, xshift=5pt]{pic cs:a4}) -- ({pic cs:b4});
   \draw [->] ([yshift=0pt, xshift=5pt]{pic cs:a5}) -- ({pic cs:b5});
   \draw [->] ([yshift=0pt, xshift=5pt]{pic cs:a6}) -- ({pic cs:b5});
   \draw [->] ([yshift=0pt, xshift=5pt]{pic cs:a7}) -- ({pic cs:b6});
   \draw [->] ([yshift=0pt, xshift=5pt]{pic cs:a8}) -- ({pic cs:b7});
   \draw [->] ([yshift=0pt, xshift=5pt]{pic cs:a9}) -- ({pic cs:b8});
   \draw [->] ([yshift=0pt, xshift=5pt]{pic cs:a10}) -- ({pic cs:b9});
   \draw [->] ([yshift=0pt, xshift=5pt]{pic cs:a11}) -- ({pic cs:b10});
   \draw [->] ([yshift=0pt, xshift=5pt]{pic cs:a12}) -- ({pic cs:b11});
\end{tikzpicture}

\end{center}
\label{default}
\end{table}

I have two questions:

• How I do make the elements in the two right columns align to the left rather than to the right?
• The table is too big to fit the page - you can see the page number 29 at the bottom of the table. How could I resize or scale it to fit the page?

Answer 1

Like this:

Your code snippet without preamble, without \newcommands you use ... isn't very helpful, so the following MWE is based on guessing, how you actually generate provided picture:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc,tikzmark}
\newcolumntype{R}{>{\raggedleft\arraybackslash}X}
\newcommand\Sq{\mathrm{Sq}}

\usepackage{showframe}

\begin{document}
\begin{table}
    \centering
\begin{tabularx}{\textwidth}{l>{\setlength\hsize{0.4\hsize}$}R<{$}
                              >{\setlength\hsize{0.2\hsize}}X
                              >{\setlength\hsize{0.4\hsize}$}R<{$}
                            }
\toprule
\multicolumn{1}{c}{Degree} 
    &   \multicolumn{2}{c}{$H^*(K(Z_2,n+1);Z_2)$} 
                                             &   H^*(K(Z,n);Z_2)                \\
\midrule
n   &   \iota_n                             &&                                  \\
n+1 & \iota_{n+1} \tikzmark{a1}             &&                                  \\
n+2 & \Sq^1\iota_{n+1} \tikzmark{a2}        && \tikzmark{b1} \Sq^2\iota_n       \\
    \addlinespace[1em]
n+3 & \Sq^2\iota_{n+1}                      && \tikzmark{b2} \Sq^3\iota_n       \\
    & \Sq^2\Sq^1\iota_{n+1}                 &&                                  \\
    \addlinespace[1em]
n+4 & \Sq^3\iota_{n+1}                      && \Sq^4\iota_n                     \\
 & \Sq^2\Sq^1\iota_{n+1} \tikzmark{a3}      &&                                  \\
    \addlinespace[1em]
n+5 & \Sq^4\iota_{n+1} \tikzmark{a4}        && \tikzmark{b3} \Sq^5\iota_n       \\
    & \Sq^3\Sq^1\iota_{n+1}                 &&                                  \\
    \addlinespace[1em]
n+6 & \Sq^5\iota_{n+1} \tikzmark{a5}        && \Sq^6\iota_{n+1}                 \\
    & \Sq^4\Sq^1\iota_{n+1} \tikzmark{a6}   && \tikzmark{b4} \Sq^4\Sq^2\iota_n  \\
    \addlinespace[1em]
n+7 & \Sq^6\iota_{n+1} \tikzmark{a7}        && \Sq^7\iota_n                     \\
    & \Sq^5\Sq^1\iota_{n+1}                 && \tikzmark{b5} \Sq^5\Sq^2\iota_n  \\
    & \Sq4\Sq^2\iota_{n+1}                  &&                                  \\
    \addlinespace[1em]
n+8 & \Sq^7\iota_{n+1} \tikzmark{a8}        && \Sq^8\iota_n                     \\
    & \Sq^6\Sq^1\iota_{n+1} \tikzmark{a9}   && \tikzmark{b6} \Sq^6\Sq^2\iota_n  \\
    & \Sq^5\Sq^2\iota_{n+1}                 &&                                  \\
    & \Sq^4\Sq^2\Sq^1\iota_{n+1} \tikzmark{a10} &&                              \\
    \addlinespace[1em]
n+9 & \Sq^8\iota_{n+1} \tikzmark{a11}       && \tikzmark{b7} \Sq^9\iota_n       \\
    & \Sq^7\Sq^1\iota_{n+1} \tikzmark{a12}  && \tikzmark{b8} \Sq^7\Sq^2\iota_n  \\
    & \Sq^6\Sq^2\iota_{n+1}                 && \tikzmark{b9} \Sq^6\Sq^3\iota_n  \\
    & \Sq^5\Sq^2\Sq^1\iota_{n+1}            &&                                  \\
    \addlinespace[1em]
n+10 & \Sq^{9}\iota_{n+1}                   && \Sq^{10}\iota_n                  \\
    & \Sq^8\Sq^1\iota_{n+1}                 && \tikzmark{b10} \Sq^8\Sq^2\iota_n \\
    & \Sq^7\Sq^2\iota_{n+1}                 && \tikzmark{b11} \Sq^7\Sq^3\iota_n \\
    & \Sq^6\Sq^3\iota_{n+1}                 &&                                  \\
    & \Sq^6\Sq^2\Sq^1\iota_{n+1}            &&                                  \\
\bottomrule
\end{tabularx}

\begin{tikzpicture}[overlay, remember picture, 
                    shorten >=5pt, shorten <=5pt]
\foreach \i [count=\j from 0] in {1,...,12} 
{
    \ifnum\i<6
\draw [->] (pic cs:a\i) -- (pic cs:b\i);
    \else
\draw [->] (pic cs:a\i) -- (pic cs:b\j);
    \fi
}
    \end{tikzpicture}

    \label{default}
\end{table}
    \end{document}

Edit (1): I also improve TikZ code. Now is more consistent and concise.

Edit (2): After re-inspection of table code redesign a table. With added empty dummy column is obtained better centering columns heads.