Question:
When making reference to the nifter during keil malei rachamim is it ploni ben/bas mother or father?
Answer:
Thank you for your question.
The Ashkenazi minhag (including chassidim) is to use the father's name, and the Sefardic minhag is to use the mothers name.
Best wishes
Sources:
Gesher Hachayim 31-2,3, Aveilus Bhalacha 43-5.