What was the last plague that induced Pharaoh to free the people of Israel from slavery in Egypt?

Answer 1

We don't know for sure when any of the plagues took place. The last plague was the death of the first born.
Makat bechorot = the slaying of the first born.
The last plague that happened before the Exodus from Egypt was the death of the firstborn males.
The death of the first born

Answer 2

Death of the Egyptian firstborn sons.

In the Exodus, Moses brought the Israelites out of the Egyptian slavery under the guidance of God, after God brought plagues upon the Egyptians (Exodus ch.1-12). After the Israelites left, Egypt was in turmoil for decades. Though Israel was later harassed (Judges ch.3,6 and 10) by its smaller neighbors (Ammon, Moab, Midian), not a peep was heard from Egypt for four hundred years.

Egypt's turmoil is also borne out by the Ipuwer papyrus, which mentions a number of the Plagues ("Pestilence is throughout the land....the river is blood, death is not scarce...there is no food...neither fruit nor herbs can be found...barley has perished...all is ruin...the statues are burned") (Professor John van Seters, Journal of Egyptian Archaeology no. 50). The plagues were also described by ancient historians, including Herodotus and Diodorus. The Exodus is mentioned by Strabo, Berosus, Artapanus, Numenius, Justin, and Tacitus.

Answer 3

Death of the Egyptian firstborn sons. See also the Related Links.

Link: Archaeology and the Hebrew Bible

Link: The Plagues

Link: The Exodus

Answer 4

Death of the First Born, of both people and animal (except among the Hebrews).

Answer 5

The plague on the first borns