Is Zakat obligatory upon a mother who owns an investment certificate exceeding the Zakat threshold, and she spends its returns on the education of her orphaned children? And is it permissible to consider the educational expenses as Zakat for the investment certificate?

If the profit from investment certificates results from usurious transactions, then it is ill-gotten wealth (mal khabith), and no zakat is due on it. Only the principal amount is subject to zakat, and the profit must be disposed of by spending it on the welfare of Muslims. However, if the profit results from Shariah-compliant transactions, then zakat is due on both the profit and the principal amount together, every lunar year. It is not permissible for a mother to pay zakat from her wealth to her poor children, because their financial support is obligatory upon her.