Is it permissible for the members of the board of trustees of a hospital, whose construction has not been completed, to donate the remaining amount from the popular committees' contributions to another public project, such as a school?

The basic principle is to spend donated funds for the specific purpose for which they were designated. It is not permissible to spend them on anything else without the donor's approval. However, if the donation was made to a general entity without a specific designation, then the money may be spent on what is most beneficial and useful for that entity.