Bearing in mind that Par'oh was speaking to Moshe and Aharon, why did he ask for forgiveness in the singular ("Sa")?
As well as the whole of Egypt - See later, Sh'mos 11:3 (Ramban).
Oznayim la'Torah: He nevertheless realized his mistake and ended in the plural "ve'Ha'atiru el Hashem.
Already in the previous Pasuk he placed Moshe and Aharon on a par with the Hashem, as he did again in this Pasuk; See Ramban. See also above, 7:1.
Why did Pharaoh say "ha'Maves ha'Zeh"? He did not say so about the frogs, which entered their bodies and croaked!