Is zakat due on money invested in commercial murabaha, or only on the 10% profits, especially since these profits are the sole means of support due to difficult circumstances?

If the money is invested in Mudarabah (definition) (a form of partnership where one party provides the capital and the other provides labor), Zakat (definition) is obligatory on the principal capital once it reaches the Nisab (definition) (minimum threshold) and a Hawl (one lunar year) has passed. It is also obligatory on the profit, even if a Hawl has not passed on it, because it follows its origin. The Nisab for banknotes is the equivalent of 85 grams of gold or 595 grams of silver, and a quarter of a tenth (2.5%) must be given out.