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.

[Q]: Passage: Glass has the ability to refract, reflect, and transmit light following geometrical optics, without scattering it. It is used in the manufacture of lenses and windows. Common glass has a refraction index around 1.5. This may be modified by adding low-density materials such as boron, which lowers the index of refraction (see crown glass), or increased (to as much as 1.8) with high-density materials such as (classically) lead oxide (see flint glass and lead glass), or in modern uses, less toxic oxides of zirconium, titanium, or barium. These high-index glasses (inaccurately known as "crystal" when used in glass vessels) cause more chromatic dispersion of light, and are prized for their diamond-like optical properties.
[A]: What can be used to make glass less dense?


[Q]: Passage: The campus also houses several performing arts facilities. The de Jong Concert Hall seats 1282 people and is named for Gerrit de Jong Jr. The Pardoe Theatre is named for T. Earl and Kathryn Pardoe. Students use its stage in a variety of theatre experiments, as well as for Pardoe Series performances. It seats 500 people, and has quite a large stage with a proscenium opening of 19 by 55 feet (17 m). The Margetts Theatre was named for Philip N. Margetts, a prominent Utah theatre figure. A smaller, black box theater, it allows a variety of seating and staging formats. It seats 125, and measures 30 by 50 feet (15 m). The Nelke Theatre, named for one of BYU's first drama teachers, is used largely for instruction in experimental theater. It seats 280.
[A]: What is named after T. Earl and Gerrit de Jong Jr.?


[Q]: Passage: Alloys are often made to alter the mechanical properties of the base metal, to induce hardness, toughness, ductility, or other desired properties. Most metals and alloys can be work hardened by creating defects in their crystal structure. These defects are created during plastic deformation, such as hammering or bending, and are permanent unless the metal is recrystallized. However, some alloys can also have their properties altered by heat treatment. Nearly all metals can be softened by annealing, which recrystallizes the alloy and repairs the defects, but not as many can be hardened by controlled heating and cooling. Many alloys of aluminium, copper, magnesium, titanium, and nickel can be strengthened to some degree by some method of heat treatment, but few respond to this to the same degree that steel does.
[A]:
what is made to stabalize the properties of base metals?