How to get figure onto same page as text

Question

I am writing a lab report introduction and am showing a figure of the reaction path. The image is very small and only requires the space of about 10 lines of text. However, when typesetting, Latex formats the figure so it is on a separate page, which looks very silly. How can I get the figure so be on the same page as the introduction paragraph?

\documentclass[11pt]{article}
\usepackage[margin=1in]{geometry}          
\usepackage{graphicx}
\usepackage{setspace}\onehalfspacing
\usepackage{float}

\begin{document}

\title{Experiment 3}

\author{Sophie Parsons%
  \thanks{CRSid: \texttt{bb70}}}
\affil{university}


\date{Dated: \today}

\maketitle



\section{Introduction}
In the reactor, the benzene and maleic anhydride can also degrade into other useless products, as shown in figure \ref{fig:7}.

\begin{figure}[H]
\begin{center}
\includegraphics[scale=0.8]{scheme.pdf}
\caption{default}
\label{fig:7}
\end{center}
\end{figure}

\end{document}

Answer 1

your image you can generate with the following small document:

\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{arrows.meta, 
                chains,
                decorations.markings,
                positioning,
                quotes,
                }

\begin{document}
    \begin{tikzpicture}[
            > = Triangle,
   decoration = {markings,% switch on markings
                 mark=at position 0.5 with {\arrow[thick]{>}}
                 },
     N/.style = {on chain},
node distance = 7mm and 21 mm,
    start chain = going right
                    ]
\node (a) [N]   {A};
\node (b) [N]   {B};
\node (c) [N]   {C};
%
\coordinate[below=of a] (aux);
\draw[postaction={decorate}]    (a) to ["$k_1$"]    (b);
\draw[postaction={decorate}]    (b) to ["$k_2$"]    (c);
\draw[postaction={decorate}]    (a) -- (aux) to ["$k_3$" '] (aux -| c) -- (c);
    \end{tikzpicture}
\end{document}

or include its code directly to your document:

\documentclass[11pt]{article}
\usepackage[margin=1in]{geometry}
\usepackage{graphicx}
\usepackage{setspace}\onehalfspacing
\usepackage{tikz} % <--- added
\usetikzlibrary{arrows.meta,         % <--- added
                chains,              % <--- added
                decorations.markings,% <--- added
                positioning,         % <--- added
                quotes,              % <--- added
                }

\begin{document}

\title{Experiment 3}
\author{Sophie Parsons%
  \thanks{CRSid: \texttt{bb70}}}
%\affil{university}
\date{Dated: \today}
\maketitle


\section{Introduction}
In the reactor, the benzene and maleic anhydride can also degrade into other useless products, as shown in figure \ref{fig:7}.
    \begin{figure}[ht]
\centering% <--- changed
        \begin{tikzpicture}[  % <--- added, instead of includegraphics
                > = Triangle,
       decoration = {markings,% switch on markings
                     mark=at position 0.5 with {\arrow[thick]{>}}
                     },
         N/.style = {on chain},
    node distance = 7mm and 21 mm,
        start chain = going right
                        ]
    \node (a) [N]   {A};
    \node (b) [N]   {B};
    \node (c) [N]   {C};
    %
    \coordinate[below=of a] (aux);
    \draw[postaction={decorate}]    (a) to ["$k_1$"]    (b);
    \draw[postaction={decorate}]    (b) to ["$k_2$"]    (c);
    \draw[postaction={decorate}]    (a) -- (aux) to ["$k_3$" '] (aux -| c) -- (c);
        \end{tikzpicture}
\caption{default}
\label{fig:7}
    \end{figure}
\end{document}

and obtain:

note:

• instead of tikz package, you can use pstric (with latter i'm not familiar)
• image generated in separate document (its name is name of image, if you like to include as .pdf image) or with code by which you replace \includegraphics{...} hasn't spurious space around it. consequently it should be on the same page as they are inserted in text (with exception, that it is inserted till before bottom of page).
• i drown this image for fun and exercise. if you have question about tikz, don't hesitate to ask new questions ...