Number Post - Home, Cat, Individual Cat

function hwl_home_pagesize( $query ) {
    if ( is_admin() || ! $query->is_main_query() )
        return;

    if ( is_home() ) {
        // Display only 3 posts 
        $query->set( 'posts_per_page', 3 );
        return;
    }    

if ( is_category( '3' ) ) {
        // Display only 2 posts 
        $query->set( 'posts_per_page', 2 );
        return;
    }

if ( is_archive() ) {
        // Display only 5 posts 
        $query->set( 'posts_per_page', 5 );
        return;
    }
}
add_action( 'pre_get_posts', 'hwl_home_pagesize', 1 );