instruction:
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.
question:
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.
answer:
What can be used to make glass less dense?

question:
Passage: Code points in the range U+D800U+DBFF (1,024 code points) are known as high-surrogate code points, and code points in the range U+DC00U+DFFF (1,024 code points) are known as low-surrogate code points. A high-surrogate code point (also known as a leading surrogate) followed by a low-surrogate code point (also known as a trailing surrogate) together form a surrogate pair used in UTF-16 to represent 1,048,576 code points outside BMP. High and low surrogate code points are not valid by themselves. Thus the range of code points that are available for use as characters is U+0000U+D7FF and U+E000U+10FFFF (1,112,064 code points). The value of these code points (i.e., excluding surrogates) is sometimes referred to as the character's scalar value.
answer:
What is a low-surrogate followed by a high-surrogate called?

question:
Passage: In May 2008 Microsoft announced that 10 million Xbox 360s had been sold and that it was the "first current generation gaming console" to surpass the 10 million figure in the US. In the US, the Xbox 360 was the leader in current-generation home console sales until June 2008, when it was surpassed by the Wii. The Xbox 360 has sold a total of 870,000 units in Canada as of August 1, 2008. Between January 2011 and October 2013, the Xbox 360 was the best-selling console in the United States for these 32 consecutive months.
answer:
How many consoles did Wii sell in 2008?