Is it permissible for me to perform Hajj on behalf of my mother using the Zakah (obligatory charity) due on my money?
It is not permissible for you to assign a portion of the Zakah due on your money for performing Hajj on behalf of your deceased mother. This is because she might have left behind an estate, in which case performing Hajj on her behalf should be funded out of it. If she left no estate, Hajj is not obligatory on her as she did not have the ability to perform it. Hajj is obligatory only on those who can afford its expenses. Allah (Exalted be He) says:
And Hajj (pilgrimage to Makkah) to the House (Ka‘bah) is a duty that mankind owes to Allâh, for those who are able to undertake the journey.
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.