%
%--------------------------------------------------------------------------------------------------------- %
\documentclass{book}
%--------------------------------------------------------------------------------------------------------- %
%
\usepackage[fleqn]{amsmath} %
\usepackage{amsthm,amssymb} %
\usepackage[paperwidth=170mm,paperheight=240mm,textwidth=132mm,driver=none,lmargin=25mm,vmargin=20mm,showframe,showcrop]{geometry} % verbose,showcrop,showframe=inner frame
\usepackage[a4,frame,center]{crop} % pageframe
%
\setlength{\marginparsep}{0mm} %
%
\renewcommand{\subQuestionNB}{\alph{subQuestion}) }

\par\nopagebreak\medskip}

\setlength{\subQuestionIndent}{26pt}

\renewcounter{Exercise}[chapter] % Reset counter every chapter
\newcounter{Problem}[chapter] %
%
%
\begin{document}

\begin{Exercise}[label={chap_01_sec_01},name={Exercises on section},counter={Problem}]
\Question{What is the symbol for iron?}
\Question{What is the symbol for hydrogen?}
\end{Exercise}

\begin{Exercise}[label={chap_01_sec_02},name={Exercises on section},counter={Problem}]
\Question{What is the symbol for lead?}
\Question{For hydrogen, state the atomic number}
\end{Exercise}

\begin{Exercise}[label={chap_02_sec_01},name={Exercises on section},counter={Problem}]
\Question{What is the symbol for copper?}
\Question{What is the form of oxygen?}
\end{Exercise}

\begin{Exercise}[label={chap_02_sec_02},name={Exercises on section},counter={Problem}]
\Question{What is the symbol for zinc?}
\Question{What is the form of zinc}
\end{Exercise}
%
% There are four sets of answers that follow
% The first two sets belong to chapter 1, the second two sets to chapter 2
%
% I want a chapter 1 header to go here
%
\Question{Fe=iron}
\Question{H}

\Question{1}

% and a chapter 2 header to go here

\Question{Cu=copper}
\Question{oxygen is a gas}

\Question{Zn=zinc}
\Question{zinc is a metal}

\end{document}

• Maybe you can reduce your code to a minimum and try to clarify your problem. At the moment, at least I, do not understand what you want. Commented May 3, 2017 at 18:16
• The answers resulting from \shipoutAnswer appear as one block without any headers to indicate which of the two chapters they belong. I want a header, say, Answers to Chapter 1, then later Answers to Chapter 2. Commented May 4, 2017 at 0:44
• I think there must be a suitable command that is understood within the exercise environment, but I cannot find it. Commented May 4, 2017 at 10:55
• Again, I think you should delete all code that is not relevant to the problem. At the moment there is much irrelevant code. And it's easier if you change your question and don't clarify it within a comment. Commented May 4, 2017 at 18:30
• OK. I can remove the unwanted code, but I'm not sure how to change the question within Stack Exchange. Would it be acceptable to start again and open a revised question? Commented May 5, 2017 at 2:56

I've created two commands:

1. \answerheaderchap{\ref{chap:...}} to put before the first answer of a chapter with the \ref{chap:...} to that chapter (of course, put the corresponding \label{chap:...} after the \chapter command)
2. \restoreanswerheader to put after the first answer of the chapter.

I've also inserted an unnumbered chapter title (if you like) before the list of the answer.

%
%--------------------------------------------------------------------------------------------------------- %
\documentclass{book}
%--------------------------------------------------------------------------------------------------------- %
%
\usepackage[fleqn]{amsmath} %
\usepackage{amsthm,amssymb} %
\usepackage[paperwidth=170mm,paperheight=240mm,textwidth=132mm,driver=none,lmargin=25mm,vmargin=20mm,showframe,showcrop]{geometry} % verbose,showcrop,showframe=inner frame
\usepackage[a4,frame,center]{crop} % pageframe
%
\setlength{\marginparsep}{0mm} %
%
\renewcommand{\subQuestionNB}{\alph{subQuestion}) }

\par\nopagebreak\medskip}

\setlength{\subQuestionIndent}{26pt}

\renewcounter{Exercise}[chapter] % Reset counter every chapter
\newcounter{Problem}[chapter] %
%
%
\begin{document}

\begin{Exercise}[label={chap_01_sec_01},name={Exercises on section},counter={Problem}]
\Question{What is the symbol for iron?}
\Question{What is the symbol for hydrogen?}
\end{Exercise}

\begin{Exercise}[label={chap_01_sec_02},name={Exercises on section},counter={Problem}]
\Question{What is the symbol for lead?}
\Question{For hydrogen, state the atomic number}
\end{Exercise}

\begin{Exercise}[label={chap_02_sec_01},name={Exercises on section},counter={Problem}]
\Question{What is the symbol for copper?}
\Question{What is the form of oxygen?}
\end{Exercise}

\begin{Exercise}[label={chap_02_sec_02},name={Exercises on section},counter={Problem}]
\Question{What is the symbol for zinc?}
\Question{What is the form of zinc}
\end{Exercise}
%
% There are four sets of answers that follow
% The first two sets belong to chapter 1, the second two sets to chapter 2
%
% I want a chapter 1 header to go here
%
\Question{Fe=iron}
\Question{H}

\Question{1}

% and a chapter 2 header to go here
\Question{Cu=copper}
\Question{oxygen is a gas}