Apply different Class for each element in a foreach()

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Firstly, you should never use query_posts to construct custom queries. This is not just my emphasis, but the codex as well. The one big problem with query_posts is, it many circumstances, pagination fails

Note: This function isn’t meant to be used by plugins or themes. As explained later, there are better, more performant options to alter the main query. query_posts() is overly simplistic and problematic way to modify main query of a page by replacing it with new instance of the query. It is inefficient (re-runs SQL queries) and will outright fail in some circumstances (especially often when dealing with posts pagination).

Just a point of note, your next_posts_link $max_pages parameter should be set for custom queries, otherwise it will fail

You should always construct custom queries with WP_Query. So your custom query should look like this

$paged = ( get_query_var('paged') ) ? get_query_var('paged') : 1;

$args = array(
    'paged'          => $paged,
    'orderby' => 'ID',
    'order' => 'DESC',
    'cat' => 50,
    'posts_per_page'    => 20,
    'post_status'      => 'publish',
    'suppress_filters' => true
);                      

$blogPosts = new WP_Query( $args );

if ( $blogPosts->have_posts() ) : while ( $blogPosts->have_posts() ) : $blogPosts->the_post();

<----YOUR LOOP---->

endwhile;

// next_posts_link() usage with max_num_pages
next_posts_link( 'Older Entries', $blogPosts->max_num_pages );
previous_posts_link( 'Newer Entries' );

wp_reset_postdata();

endif;

Lastly, your counter should start outside the loop, not inside

if ( $blogPosts->have_posts() ) : 
    $count = 0;
    while ( $blogPosts->have_posts() ) : $blogPosts->the_post();

EDIT

Custom pagination function. I don’t know who the original author of this function is, but thanks to you if you ever find this answer 🙂

function custom_pagination($pages="", $range = 2) {   
   $showitems = ($range * 2)+1;  

  global $paged;
  if(empty($paged)) $paged = 1;

      if($pages == '')
      {
         global $wp_query;
         $pages = $wp_query->max_num_pages;
            if(!$pages)
            {
            $pages = 1;
            }
        }   

       if(1 != $pages)
      {
        $string = _x( 'Page %1$s of %2$s' , '%1$s = current page, %2$s = all pages' , 'pietergoosen' );
        echo "<div class="pagination"><span>" . sprintf( $string, $paged, $pages ) . "</span>";
          if($paged > 2 && $paged > $range+1 && $showitems < $pages) echo "<a href="".get_pagenum_link(1)."">" . __( '&laquo; First', 'pietergoosen' ) . "</a>";
         if($paged > 1 && $showitems < $pages) echo "<a href="".get_pagenum_link($paged - 1)."">" . __( '&lsaquo; Previous', 'pietergoosen' ) . "</a>";

            for ($i=1; $i <= $pages; $i++)
            {
               if (1 != $pages &&( !($i >= $paged+$range+1 || $i <= $paged-$range-1) || $pages <= $showitems ))
               {
                    echo ($paged == $i)? "<span class=\"current\">".$i."</span>":"<a href="".get_pagenum_link($i)."" class=\"inactive\">".$i."</a>";
               }
           }

           if ($paged < $pages && $showitems < $pages) echo "<a href="" . get_pagenum_link($paged + 1)."">" . __( 'Next &rsaquo;', 'pietergoosen' ) . "</a>";
           if ($paged < $pages-1 &&  $paged+$range-1 < $pages && $showitems < $pages) echo "<a href="".get_pagenum_link($pages)."">" . __( 'Last &raquo;', 'pietergoosen' ) . "</a>";
           echo "</div>\n";
     }
    } //