Just an FYI for more advanced usage cases, for example where you have multiple repeaters on the same page in flexible content and you need unique ID’s for each block(for example to target bootstrap modals or collapse elements) you can do something like this:
<section class="faq-block <?php if (get_sub_field('background') == 'blue'): ?> blue-bg<?php else: ?><?php endif; ?>">
<div class="container">
<div class="row text-center">
<div class="col-md-10 col-md-offset-1">
<h2 class="section-heading"><?php the_sub_field( 'section_heading' ) ?></h2>
<div class="panel-group" id="accordion" role="tablist" aria-multiselectable="true">
<?php
//$uniqueid = get_sub_field( 'faq_unique_id' );
$uniqueid = uniqid('faq_items');
$count = 0;
while ( have_rows( 'faq_items' ) ) : the_row(); ?>
<div class="panel panel-default listbox">
<div class="panel-heading" role="tab" id="headingTwo">
<h3 class="panel-title">
<a data-toggle="collapse" data-parent="#accordion"
href="#collapse-<?php echo esc_attr( $uniqueid ); ?>-<?php echo esc_attr( $count ); ?>"
aria-expanded="false">
<?php the_sub_field( 'faq_question' ) ?>
</a>
</h3>
</div>
<div id="collapse-<?php echo esc_attr( $uniqueid ); ?>-<?php echo esc_attr( $count ); ?>"
class="panel-collapse collapse" role="tabpanel">
<div class="panel-body">
<p><?php the_sub_field( 'faq_answer' ) ?></p>
</div>
</div>
</div>
<?php $count ++; ?>
<?php endwhile; ?>
</div><!--end panel group-->
</div>
</div>
</div>
</section>
