As for the Zalzalah, the hadeeth is weak and not authentic. As for the Kafiroon, it is authentic as was authenticated by Sheikh Al Albani.

I have heard that Surat Al Zalzala is equivalent to a half of the Qur’an, and that Surat Al Kafiroon is equivalent to a quarter of the Qur’an. Is there any hadith sahih which proves this statement