D should be it.
(A) at its 1833 founding for deciding to accept
-weird construction. Looks like 1833 is the no of foundings, rather than year of founding..
(B) for the decision at its 1833 founding to accept
-weird construction. same as A
(C) when it was founded in 1833 for its decision to accept
- Looks bad also. Seems to indicate that it was founded because it decided to accept both men and women as students.
(D) in deciding at its founding in 1833 to accept
- Clear meaning. Indicates when it was founded and what actions were taken.
(E) by deciding at its founding in 1833 on the acceptance of
- Total mess