Were the Jews slaves in Egypt?

A: No. neither the Jews nor their Hebrew ancestors were slaves in Egypt. Almost all scholars now acknowledge that there was no Exodus from Egypt as described in the Bible, and no conquest of Canaan. The story of the Israelites as slaves in Egypt might have a germ of historical truth: for example it has been suggested that a small band of slaves escaped and travelled through Midian and then to Judah, where they settled among the Jews already there.
Answer:
Yes, of course the Jews (Israelites) were slaves in Egypt. This is stated in the Torah (Exodus ch.1) again (Exodus ch.20) and again (Leviticus 26:13) and again (Numbers 20:15) and again (Deuteronomy 5:6). This is one of the fundamental underpinnings of Judaism, since many of the commands are tied to the Exodus (Exodus ch.12-13, Leviticus 11:45, 19:36, 25:38, Deuteronomy 16:1).

The Ipuwer papyrus describes Egypt's experiencing 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.

Yes. The Ipuwer papyrus describes Egypt's experiencing 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).

• Link: More on the topic
  

The plagues were also described by ancient historians, including Herodotus and Diodorus. The Exodus is mentioned by Strabo, Berosus, Artapanus, Numenius, Justin, and Tacitus.

• Link: Evidence of the Exodus
  

But in any case, few nations are content to record embarrassing setbacks honestly. Even today, British and American textbooks describe the American Revolution in very different ways.

An example of the above principle:

The destruction of Sennacherib's army at the walls of Jerusalem was denied by secular theorists, because the Assyrians made no mention of it. But then it was found that Berosus and Herodotus both state that Sennacherib's military campaign in Judea ended in plague and defeat. It should not surprise us that the Assyrians themselves didn't record their own losses.

It is only the Hebrew Bible, because of its Divine origin, that exposes the faults of its own people and even magnifies them.

In no other religious text can one find such openness. None of the Israelites were immune to strong criticism: Abraham (Genesis 16:5), Reuben (Gen.ch.35), Simeon and Levi (Gen.ch.34 and 49), Judah (Gen.ch.38), Joseph's brothers (Gen.ch.37), Moses (Numbers ch.20), Aaron (Exodus 32:2-4), Samson (Judges 14:1-3), Eli's sons (1 Samuel 2:12), Samuel's sons (1 Samuel 8:1-3), Saul (1 Samuel ch.15), David (2 Samuel ch.11-12), Solomon (1 Kings ch.11), and many others.

See also the Related Links.

Link: Is the Hebrew Bible accurate?

Link: Moses was a real person