How can it to be that only five horses remained in Shomron?
Radak citing his father: Just like almost all the people died, almost all the horses died.
What is the meaning of "Nish'arah Vah"?
Rashi: They remain in the city; they did not starve.
Why did he say "k'Chol Hamon Yisrael"?
Rashi: If you will say that they are in danger lest people kill them, also in the city there is danger of starvation, like all of Yisrael!
Radak: They are weak, like all Yisrael remaining in Shomron who are weak from hunger.
Radak citing Targum Yonasan: If they will die, they will be like the multitudes of Yisrael who died.
Malbim: They are like all Yisrael, who are destined to die from hunger.
Why is it written ha'Hamon, and we pronounce it Hamon?
Radak: It is written with the prefix Hei to identify, even though it is Samuch, like "ha'Am ha'Milchamah", "ha'Aron ha'Bris" (Yehoshua 8:11, 3:14) and similar verses. We pronounce it without the Hei, like usually it is omitted (when it is Samuch.