1) The wedding cake was baked by the famous cook who lives in Minsk. - страдательный залог - испечен кем?
2) An interesting newspaper has been read by me this week. - артикль необходим, а предлог не нужен ни в коем случае
3) The floor of my room will be painted tomorrow. - родительный падеж
4) The dirty WC has been cleaned with a cleanser. - очищающим средством, а "вмятина" не нужна, я думаю
5) The orchids would be watered by our neighbors. - в слове "орхидеи" пропущена буква, пропущен предлог by - страдательный залог