With geometry
for smaller margins, a slightly smaller \tabcolsep
and the help of an abbreviation you can get the following:

\documentclass{article}
\usepackage[usenames,dvipsnames]{xcolor}
%\usepackage[table,svgnames]{xcolor}
\usepackage[many]{tcolorbox}
\tcbuselibrary{skins}
\usepackage{tabularx}
\usepackage{array}
\usepackage{colortbl}
\usepackage{geometry}
\usepackage{array,multirow,tabularx}
\newcolumntype{Y}{>{\centering\arraybackslash}X}
\tcbset{tab2/.style={enhanced,fonttitle=\bfseries,fontupper=\normalsize\sffamily,
colback=white!10!white,colframe=red!50!black,colbacktitle=Salmon!40!white,
coltitle=black,center title}}
\begin{document}
\begin{table}[htb]
\setlength{\tabcolsep}{5pt}
\refstepcounter{table}
\begin{tcolorbox}[tab2,tabularx*={\renewcommand{\arraystretch}{1.5}}{c|Y|Y|Y|Y|Y|Y|Y|Y|Y|Y},title={Table \thetable. This is a table},boxrule=0.8pt]
& \multicolumn{5}{c|}{Year 1} & \multicolumn{5}{c|}{Year 2}\\ \hline
& \multicolumn{2}{c|}{Part-B}& \multicolumn{2}{c|}{Part-C} & & \multicolumn{2}{c|}{Part-B}& \multicolumn{2}{c|}{Part-C} & \\ \hline
& NQ & Marks & NQ & Marks & Total & NQ & Marks & NQ & Marks & Total\\\hline
statement A & 10 & 20 & 30 & 4000 & 100& sum & sum & 60.75 & sum & 121.5\\\hline
RA & 20 & 30 & 40 & 50 & 140 & sum & 60.75 & sum & 60.75 & 71.5\\\hline
LA & 30 & 40 & 50 & 60 & 180 & sum & 60.75 & sum & 60.75 & 60.75\\\hline
statement B & 60 & 90 & 120 & 150 & 420& 60.75 & 60.75 & sum & 60.75 & sum\\\hline
\multicolumn{11}{l}{NQ = Number of Questions}\\
\end{tcolorbox}
\end{table}
\end{document}
Similar idea as above but without the geometry
package:

\documentclass{article}
\usepackage[usenames,dvipsnames]{xcolor}
%\usepackage[table,svgnames]{xcolor}
\usepackage[many]{tcolorbox}
\tcbuselibrary{skins}
\usepackage{tabularx}
\usepackage{array}
\usepackage{colortbl}
\usepackage{array,multirow,tabularx}
\newcolumntype{Y}{>{\centering\arraybackslash}X}
\tcbset{tab2/.style={enhanced,fonttitle=\bfseries,fontupper=\normalsize\sffamily,
colback=white!10!white,colframe=red!50!black,colbacktitle=Salmon!40!white,
coltitle=black,center title}}
\begin{document}
\begin{table}[htb]
\setlength{\tabcolsep}{3pt}
\refstepcounter{table}
\begin{tcolorbox}[tab2,tabularx*={\renewcommand{\arraystretch}{1.5}}{|Y|c|c|c|c|c|c|c|c|c|c|},title={Table \thetable. This is a table},boxrule=0.8pt]
& \multicolumn{5}{c|}{Year 1} & \multicolumn{5}{c|}{Year 2}\\ \hline
& \multicolumn{2}{c|}{Part-B}& \multicolumn{2}{c|}{Part-C} & & \multicolumn{2}{c|}{Part-B}& \multicolumn{2}{c|}{Part-C} & \\ \hline
& NQ & Marks & NQ & Marks & Total & NQ & Marks & NQ & Marks & Total\\\hline
statement A & 10 & 20 & 30 & 4000 & 100& sum & sum & 60.75 & sum & 121.5\\\hline
RA & 20 & 30 & 40 & 50 & 140 & sum & 60.75 & sum & 60.75 & 71.5\\\hline
LA & 30 & 40 & 50 & 60 & 180 & sum & 60.75 & sum & 60.75 & 60.75\\\hline
statement B & 60 & 90 & 120 & 150 & 420& 60.75 & 60.75 & sum & 60.75 & sum\\\hline
\multicolumn{11}{l}{NQ = Number of Questions}\\
\end{tcolorbox}
\end{table}
\end{document}
With geometry
, a smaller font size and without the abbreviation:

\documentclass{article}
\usepackage[usenames,dvipsnames]{xcolor}
%\usepackage[table,svgnames]{xcolor}
\usepackage[many]{tcolorbox}
\tcbuselibrary{skins}
\usepackage{tabularx}
\usepackage{array}
\usepackage{colortbl}
\usepackage{geometry}
\usepackage{makecell}
\usepackage{array,multirow,tabularx}
\newcolumntype{Y}{>{\centering\arraybackslash}X}
\tcbset{tab2/.style={enhanced,fonttitle=\bfseries,fontupper=\small\sffamily,
colback=white!10!white,colframe=red!50!black,colbacktitle=Salmon!40!white,
coltitle=black,center title}}
\begin{document}
\begin{table}[htb]
\setlength{\tabcolsep}{3pt}
\refstepcounter{table}
\begin{tcolorbox}[tab2,tabularx*={\renewcommand{\arraystretch}{1.5}}{c|Y|c|Y|c|c|Y|c|Y|c|c},title={Table \thetable. This is a table},boxrule=0.8pt]
& \multicolumn{5}{c|}{Year 1} & \multicolumn{5}{c|}{Year 2}\\ \hline
& \multicolumn{2}{c|}{Part-B}& \multicolumn{2}{c|}{Part-C} & & \multicolumn{2}{c|}{Part-B}& \multicolumn{2}{c|}{Part-C} & \\ \hline
& Number of \newline Qeustions & Marks & Number of \newline Qeustions & Marks & Total & Number of \newline Qeustions & Marks & Number of \newline Qeustions & Marks & Total\\
\hline
statement A & 10 & 20 & 30 & 4000 & 100& sum & sum & 60.75 & sum & 121.5\\\hline
RA & 20 & 30 & 40 & 50 & 140 & sum & 60.75 & sum & 60.75 & 71.5\\\hline
LA & 30 & 40 & 50 & 60 & 180 & sum & 60.75 & sum & 60.75 & 60.75\\\hline
statement B & 60 & 90 & 120 & 150 & 420& 60.75 & 60.75 & sum & 60.75 & sum\\\hline
\end{tcolorbox}
\end{table}
\end{document}
Without geometry
but with an even smaller font size:

\documentclass{article}
\usepackage[usenames,dvipsnames]{xcolor}
%\usepackage[table,svgnames]{xcolor}
\usepackage[many]{tcolorbox}
\tcbuselibrary{skins}
\usepackage{tabularx}
\usepackage{array}
\usepackage{colortbl}
%\usepackage{geometry}
\usepackage{makecell}
\usepackage{array,multirow,tabularx}
\newcolumntype{Y}{>{\centering\arraybackslash}X}
\tcbset{tab2/.style={enhanced,fonttitle=\bfseries,fontupper=\scriptsize\sffamily,
colback=white!10!white,colframe=red!50!black,colbacktitle=Salmon!40!white,
coltitle=black,center title}}
\begin{document}
\begin{table}[htb]
\setlength{\tabcolsep}{2pt}
\refstepcounter{table}
\begin{tcolorbox}[tab2,tabularx*={\renewcommand{\arraystretch}{1.5}}{c|Y|c|Y|c|c|Y|c|Y|c|c},title={Table \thetable. This is a table},boxrule=0.8pt]
& \multicolumn{5}{c|}{Year 1} & \multicolumn{5}{c|}{Year 2}\\ \hline
& \multicolumn{2}{c|}{Part-B}& \multicolumn{2}{c|}{Part-C} & & \multicolumn{2}{c|}{Part-B}& \multicolumn{2}{c|}{Part-C} & \\ \hline
& Number of \newline Qeustions & Marks & Number of \newline Qeustions & Marks & Total & Number of \newline Qeustions & Marks & Number of \newline Qeustions & Marks & Total\\
\hline
statement A & 10 & 20 & 30 & 4000 & 100& sum & sum & 60.75 & sum & 121.5\\\hline
RA & 20 & 30 & 40 & 50 & 140 & sum & 60.75 & sum & 60.75 & 71.5\\\hline
LA & 30 & 40 & 50 & 60 & 180 & sum & 60.75 & sum & 60.75 & 60.75\\\hline
statement B & 60 & 90 & 120 & 150 & 420& 60.75 & 60.75 & sum & 60.75 & sum\\\hline
\end{tcolorbox}
\end{table}
\end{document}