What is the question "hak'Makas Makehu Hikahu"?
Rashi: Did you see My Gevurah? Like the blow of the one who strikes Yakov, I hit him. [Egypt] drowned [babies of] Yakov in the water, and I drowned them in the water! Some questions said in astonishment remain (they are not answered), like this, and "ha'Nigleh Nigleisi El Beis Avicha" (Shmuel I, 2:27), "ha'Ro'eh Atah Mah Hem Osim" (Yechezkel 8:6).
Radak: Nowadays, you can recognize and know that Hashem has no anger against Yisrael - "Chemah Ein Li" (4). Makehu is one who strikes Yisrael, like Pharaoh, Sancheriv and others. For all that Yisrael sinned, did Hashem strike them like He struck the one who struck Yisrael, with 10 Makos?!
What is the question "Im k'Hereg Harugav Horag"?
Rashi: Like Yisrael, whom Pharaoh killed, Pharaoh and his nation will be killed.
Radak #1: The matter is repeated. Were Yisrael killed, like those who killed Yisrael were killed, i.e. Yisrael's enemies? "Harugav" are those that Hashem 1 killed due to Yisrael.
Radak #2: "Harugav" refers to Yisrael, Since they were killed due to Yisrael, it is as if Yisrael killed them.
Malbim: Did Hashem kill Yisrael like He did (totally wiped out) the murderers among the nation that struck Yisrael?
The text should say that the pronoun (suffix) refers to Kel, like Kli Paz cites it.
