I am facing problem for spacing for number and text in TOC.
The are very close after second digit.
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\documentclass[a4paper,12pt,openany]{book} %openany is for removing blank page between two chapter
\usepackage[a4paper, top=1 in, bottom=1 in,textwidth=6.52in]{geometry} %to get normal margin, remove textwith length
%###############----FONT----#########################
\usepackage[T1]{fontenc}
\usepackage[adobe-utopia]{mathdesign}%% ADDED
\usepackage[utf8]{inputenc}
%--------------------------------------------
%-----------THIS SECTION IS ADDED FROM IIT-------------------
\usepackage{booktabs}
\usepackage{amsmath}%, amsfonts, amssymb
\usepackage{amsfonts}
\usepackage{amsthm}
\usepackage{xcolor}
\usepackage{fancyhdr}
\setlength{\headheight}{15pt} % related to fancyhdr
%------------------------------------------------------------------
\usepackage[bookmarks,%
breaklinks,%
backref=false,%
pdfhighlight=/I,%
pdffitwindow=true,%
pdfstartview=Fit,%
pdfcenterwindow=true,%
linkbordercolor={1 0 1},%
pdfusetitle]
{hyperref}
\RequirePackage{graphicx}
\usepackage{multicol} % For multiple column
\usepackage{siunitx} %for SI units
%%%%%%%%%%%%%%%%%%%%ADDED BY ME%%%%%%%%%%%%%%%%%%%%%%%
\usepackage{pifont} %for symbols in text mode
\usepackage{enumitem}
\setlist[itemize,enumerate]{noitemsep,topsep=0pt}%http://tex.stackexchange.com/questions/43743/how-to-reduce-line-space-leading-within-an-enumerate-environment
\renewcommand{\labelitemi}{\ding{70}}%https://en.wikibooks.org/wiki/LaTeX/Special_Characters
\renewcommand{\labelitemii}{\ding{118}}
\usepackage{tcolorbox} %%for coloured boxex
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Source: http://en.wikibooks.org/wiki/LaTeX/Hyperlinks %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usepackage{hyperref}
\usepackage{graphicx}
\usepackage{caption}
\usepackage{subcaption}
\usepackage[english]{babel}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% 'dedication' environment: To add a dedication paragraph at the start of book %
% Source: http://www.tug.org/pipermail/texhax/2010-June/015184.html %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\newenvironment{dedication}
{
\cleardoublepage
\thispagestyle{empty}
\vspace*{\stretch{1}}
\hfill\begin{minipage}[t]{0.66\textwidth}
\raggedright
}
{
\end{minipage}
\vspace*{\stretch{3}}
\clearpage
}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Chapter quote at the start of chapter %
% Source: http://tex.stackexchange.com/a/53380 %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\makeatletter
\renewcommand{\@chapapp}{}% Not necessary...
\newenvironment{chapquote}[2][2em]
{\setlength{\@tempdima}{#1}%
\def\chapquote@author{#2}%
\parshape 1 \@tempdima \dimexpr\textwidth-2\@tempdima\relax%
\itshape}
{\par\normalfont\hfill...\ \chapquote@author\hspace*{\@tempdima}\par\bigskip}
\makeatother
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Colour font of Chapters and sections %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\makeatletter
\usepackage{xcolor}
\usepackage{sectsty}
\usepackage{titlecaps} %http://tex.stackexchange.com/questions/129677/automatic-capitalization-of-sectioning-headings
\chapterfont{\color{blue}} % sets colour of chapters
\sectionfont{\color{blue}\titlecap} % sets colour of sections and each letter of word capital
\Addlcwords{to the of or at in and for from is} % make words in title/section small
\subsectionfont{\color{black}}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% First page of book which contains 'stuff' like: %
% - Book title, subtitle %
% - Book author name %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Book's title and subtitle
\title{\Huge \textbf{Chemical Engineering Notes}}
% Author
\author{\textsc{Dr. XYZ}}
\begin{document}
\frontmatter
\maketitle
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Add a dedication paragraph to dedicate your book to someone %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{dedication}
Dedicated to All Chemical Engineers
\end{dedication}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Auto-generated table of contents, list of figures and list of tables %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\tableofcontents
\listoffigures
\listoftables
\mainmatter
%%%%%%%%%%%
%%%%%%%%%%%%%%%%
% NEW CHAPTER! %
\chapter{Fluid Flow}
\section{Drag reduction is found generally}
\section{Drag reduction is found generally}
\section{Drag reduction is found generally}
\section{Drag reduction is found generally}
\section{Drag reduction is found generally}
\section{Drag reduction is found generally}
\section{Drag reduction is found generally}
\section{Drag reduction is found generally}
\section{Drag reduction is found generally}
\section{Drag reduction is found generally}
\section{Drag reduction is found generally}
\section{Drag reduction is found generally}
\section{Drag reduction is found generally}
\end{document}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Best Answer
This is well-known limitation of standard classes TOCs. It depends a bit on fonts used (because narrower fonts will be less likely to show the problem).
Simplest workaround is to add something like this to your preamble
For example:
Without the added lines:
With the fix: