Engulfing-phagocytic cells of innate immunity of vertebrates include i) neutrophils ii) macrophages iii) dendritic cells iv) natural killer cells

The correct answer is I, II and III.
A phagocytic cell of a vertebrate organism is a critical component of the immune system. Its main action is to engulf and ingest foreign and possibly harmful particles, bacteria and dead or dying cells.

There are many different types of phagocytes and some of these include the macrophages, the neutrophils, and the dendritic cells.
The macrophages are phagocytic cells which can exit the bloodstream and detect pathogens outside the circulatory system.
Neutrophils contain toxic granules which can kill pathogens only by contact. Dendritic cells are located in the parts of the body which can easily be infected and can act as messengers who warn the body of threats. They do so by sending antigens as messages.