What is the difference between the two and when should they be used?
Also when addressing one person what is the difference between Jazakallah Khayrun vs Jazakallah Khair?
What is the difference between the two and when should they be used?
Also when addressing one person what is the difference between Jazakallah Khayrun vs Jazakallah Khair?
As Salaamu 3laykum,
I hope you are doing well. When using Wa-iyyak or Wa-iyyakum it depends who you are addressing. In arabic there are pronouns that are attached and de-attached. In this case these are attached pronouns.
1 male - wa-iyyaka
2 males - wa-iyyakuma
3 or more males - wa-iyyakum
1 female - wa-iyyaki (kee)
2 females - wa-iyyakuma
3 or more females - wa-iyyakuna
Source: https://www.youtube.com/watch?v=eo8PC62VhNM&ab_channel=AlhudaDiaries
Regarding your second question:
The Messenger of ALLAAH (ﷺ) said, “He who is favoured by another and says to his benefactor: `Jazak-Allah khairan (may Allah reward you well)’ indeed praised (the benefactor) satisfactorily.” Riyad As-Salihin – [At-Tirmidhi]