Hi tuhinbiswas98. You can do this using the WP in_category() function.
1. Copy content-featured.php from the parent theme to your child theme.
2. At the top of the file you’ll see this block of code:
<?php if ( has_post_thumbnail() ): ?>
<?php the_post_thumbnail('thumb-large'); // only difference to content.php ?>
<?php elseif ( ot_get_option('placeholder') != 'off' ): ?>
<img src="<?php echo get_template_directory_uri(); ?>/img/thumb-medium.png" alt="<?php the_title(); ?>" />
<?php endif; ?>
3. Add one line before and one line after so you end up with this:
<?php if ( is_category('my-category') ) : ?>
<?php if ( has_post_thumbnail() ): ?>
<?php the_post_thumbnail('thumb-large'); // only difference to content.php ?>
<?php elseif ( ot_get_option('placeholder') != 'off' ): ?>
<img src="<?php echo get_template_directory_uri(); ?>/img/thumb-medium.png" alt="<?php the_title(); ?>" />
<?php endif; ?>
<?php endif; ?>
4. Change ‘my-category’ to the name of your category.