Maybe adding something like:

\settasks{
item-indent = 2em
}

could solve the indentation for the answers.

can you show me an example of where you'd put it?

i put it right after \begin{document} but it didnt help.

i tried putting an absurdly high value ( 14.33em ) and the result was as shown.

it didnt solve my issue, but it atleast clarified it somewhat, that for answers its the tasks package issue ( perhaps) and for question its AMC issue.

Sorry for the wrong advice. I normally use tasks outside of auto-multiple-choice and the item-indent is honored.
I attach a mainfile.tex where instead of using tasks and choicescustom I just use choices.
What's your aim using tasks?

\usepackage{linegoal}

\parbox[t]{\linegoal}{In nitrogen family, the \ce{H-X-H} bond angle in the hydrides gradually becomes closer to \ang{90} on going from \ce{N} to \ce{Sb}. This shows that gradually}

@rafael i use customchoices because i wanted to enumerate horizontally instead of vertically. Check out this link. [[https://tex.stackexchange.com/questions/595805/using-multicols-or-tasks-to-enumerate-horizontally-instead-of-vertically-in-auto]]

@gerard your solution helped. but instead of writing it for every question is it possible to define it for every question at the beginning of the document or something?

in addition i used choices instead of customchoices, it showed me some error of "perhaps a missing item" when i ignored the error, the output was correct.

So two questions
1. how to define the linegoal at the beginning of document?
2. is there any issue or resolution to using choices or customchoices.

how to define the linegoal at the beginning of document?

I don't know.

is there any issue or resolution to using choices or customchoices

Another idea but english language is not my native english, so may be i misunderstood your request .

\usepackage{hlist,linegoal}

\parbox[t]{\linegoal}{
In nitrogen family, the \ch{H-X-H} bond angle in the hydrides gradually becomes closer to \ang{90} on going from \ch{N} to \ch{Sb}. This shows that gradually}

\def\AMCbeginAnswer{\hlist[label=,left margin=1em]2}
\def\AMCendAnswer{\endhlist}
\begin{choicescustom}

\hitem \correctchoice{The crystal lattice of ice is mostly formed by covalent as well as hydrogen bonds}
\hitem  \correctchoice{The density of water increases when heated from  \SI{0}{\celsius} to \SI{4}{\celsius}  due to the change in the structure of the cluster of water molecules}
\hitem  \correctchoice{Above  \SI{4}{\celsius}  the thermal agitation of water molecules increases. Therefore, intermolecular  distance increase and water starts expanding}
\hitem  \correctchoice{The density of water increases from  \SI{0}{\celsius}  to a maximum at \SI{4}{\celsius}   because the entropy  (disorder) of the system increases}

\end{choicescustom}

I use chemformula package \ch{} instead mhchem \ce{}.