What is produced in innate immunity to prevent the entry of foreign agents into the body?

Antibodies produced by $B$-lymphocytes are responsible for:

Arrange the steps of the $phagocytosis$ process in the correct sequence.
$(a)$ Ingestion of microbes by phagocytes
$(b)$ Dilation of blood vessels by histamine
$(c)$ Formation of $phagosome$ and $phagolysosome$
$(d)$ Migration of phagocytes into $E.C.F.$
$(e)$ Attraction of phagocytes by $chemotoxins$ secreted by microbes
$(f)$ Intracellular destruction of bacteria

Resistance against pathogens is due to

Which is the main physical barrier in our body?

Injection of an antidote against snake-bite is an example of