Amended single.php for Ridizain

single.php

<?php
/**
 * The Template for displaying all single posts
 * This amendment is in reference to: https://wordpress.org/support/topic/query-about-ad-placement?replies=7
 *
 * @package Ridizain
 * @since Ridizain 1.0
 */

get_header(); ?>

	<div id="primary" class="content-area">
		<div id="content" class="site-content" role="main">
			<?php
				// Start the Loop.
				while ( have_posts() ) : the_post();

					/*
					 * Include the post format-specific template for the content. If you want to
					 * use this in a child theme, then include a file called called content-___.php
					 * (where ___ is the post format) and that will be used instead.
					 */
					get_template_part( 'content', get_post_format() );
					if ( function_exists( 'get_author_bio_box' ) ) {
                                              echo get_author_bio_box();
                                        } ?>
					
					<!-- Place your ad code here -->
					
					<?php wp_related_posts();

					// Previous/next post navigation.
					ridizain_post_nav();

					// If comments are open or we have at least one comment, load up the comment template.
					if ( comments_open() || get_comments_number() ) {
						comments_template();
					}
				endwhile;
			?>
		</div><!-- #content -->
	</div><!-- #primary -->

<?php
get_sidebar( 'content' );
get_sidebar();
get_footer();

This gist assumes you have copied the single.php file in to your child theme and made the amendments there.