TASK DEFINITION: This task is about creating an unanswerable question based on a given passage. Construct a question that looks relevant to the given context but is unanswerable. Following are a few suggestions about how to create unanswerable questions:
(i) create questions which require satisfying a constraint that is not mentioned in the passage
(ii) create questions which require information beyond what is provided in the passage in order to answer
(iii) replace an existing entity, number, date mentioned in the passage with other entity, number, date and use it in the question
(iv) create a question which is answerable from the passage and then replace one or two words by their antonyms or insert/remove negation words to make it unanswerable.
PROBLEM: Passage: The defence estate is divided as training areas & ranges (84.0%), research & development (5.4%), airfields (3.4%), barracks & camps (2.5%), storage & supply depots (1.6%), and other (3.0%). These are largely managed by the Defence Infrastructure Organisation.

SOLUTION: What organization do airfields manage?

PROBLEM: Passage: A team led by Enrico Fermi in 1934 observed that bombarding uranium with neutrons produces the emission of beta rays (electrons or positrons from the elements produced; see beta particle). The fission products were at first mistaken for new elements of atomic numbers 93 and 94, which the Dean of the Faculty of Rome, Orso Mario Corbino, christened ausonium and hesperium, respectively. The experiments leading to the discovery of uranium's ability to fission (break apart) into lighter elements and release binding energy were conducted by Otto Hahn and Fritz Strassmann in Hahn's laboratory in Berlin. Lise Meitner and her nephew, the physicist Otto Robert Frisch, published the physical explanation in February 1939 and named the process "nuclear fission". Soon after, Fermi hypothesized that the fission of uranium might release enough neutrons to sustain a fission reaction. Confirmation of this hypothesis came in 1939, and later work found that on average about 2.5 neutrons are released by each fission of the rare uranium isotope uranium-235. Further work found that the far more common uranium-238 isotope can be transmuted into plutonium, which, like uranium-235, is also fissile by thermal neutrons. These discoveries led numerous countries to begin working on the development of nuclear weapons and nuclear power.

SOLUTION: When was it observed that bombarding uranium with neutrons results in gamma ray emission?

PROBLEM: Passage: "By May 1539, Conquistador Hernando de Soto skirted the coast of Florida, searching for a deep harbor to land. He described seeing a thick wall of red mangroves spread mile after mile, some reaching as high as 70 feet (21 m), with intertwined and elevated roots making landing difficult. Very soon, 'many smokes' appeared 'along the whole coast', billowing against the sky, when the Native ancestors of the Seminole spotted the newcomers and spread the alarm by signal fires". The Spanish introduced Christianity, cattle, horses, sheep, the Spanish language, and more to Florida.[full citation needed] Both the Spanish and French established settlements in Florida, with varying degrees of success. In 1559, Don Tristán de Luna y Arellano established a colony at present-day Pensacola, one of the first European settlements in the continental United States, but it was abandoned by 1561.

SOLUTION:
What happened in 1538?