1)
Hat are the implications of the words "ke'Mishkav Nidasah Yiy'heh lah" in the singular)?
2)
Why does the Torah write "ke'Tum'as Nidasah" and not 'ke'Mishkav Nidasah'?
1.
Sifra: To teach us that the Bo'el Nidah adopts the Tum'ah of the Nidah, but only for one day - "ke'Tum'as Nidasah", 've'Lo ki'Yemei Nidasah'.