How to assigned specific "comment" view mode for specific "node" view mode? In "Article" content type i have three view mode in "Manage Display" namely "teaser", "default" and "abc".

Similary in "Comment Display" i have two view mode namely "defalut" and "xyz".

Eg: When i see "abc" node page where i am listing comments, that time the comment should be display with my "xyz" view mode not the "default" one. 

function custom_node_view($node) {
    return node_view($node, 'abc');
}
You could use hook_entity_view_mode_alter() to switch it on the fly.