Try using the count variable to increment the loop.
<div class="panel-group" id="accordion" role="tablist" aria-multiselectable="true">
<?php if(get_field('faq_general_ht')): ?>
<?php $count=0; ?>
<?php while(has_sub_field('faq_general_ht')): ?>
<div class="panel panel-default">
<div class="panel-heading" role="tab" id="headingTwo">
<h4 class="panel-title">
<?php echo '<a data-toggle="collapse" data-parent="#accordion" href="#collapse' .$count. '"aria-expanded="true">' ?>
<p><?php the_sub_field('faq_general_question_ht') ?></p>
</a>
</h4>
</div>
<?php echo '<div id="collapse' .$count. '" class="panel-collapse collapse" role="tabpanel">' ?>
<div class="panel-body">
<p><?php the_sub_field('faq_general_answer_ht') ?></p>
</div>
</div>
</div>
<?php $count++; ?>
<?php endwhile; ?>
<?php endif; ?>
</div>