Which one of the following statements about glass is not correct ?
- A.Glass is often said to be a supercooled liquid.
- B.Glass has no definite melting point.
- C.Soda glass is harder than pyrex glass.
- D.Boron is present in pyrex glass.
Correct answer
Explanation
The correct answer is C, Soda glass is harder than pyrex glass. This statement is wrong: soda glass is the soft glass, while pyrex is a hard borosilicate glass.
Ordinary soda-lime glass is made from silica (sand), sodium carbonate and limestone; it softens at a fairly low temperature and is used for windows, bottles and tumblers. Pyrex has boron oxide added to the silica, so it expands very little on heating, resists heat and sudden changes of temperature, and is used for laboratory apparatus and ovenware.
A is not the answer: glass is indeed often called a supercooled liquid, because it is an amorphous solid without an ordered crystal lattice.
B is not the answer: glass has no sharp melting point; it softens gradually over a range of temperatures.
D is not the answer: boron is present in pyrex, which is why it is called borosilicate glass.
Exam tip: soda-lime glass = soft glass for windows and bottles; borosilicate (pyrex) = heat-resistant laboratory glass.
Practice Questions
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- A.haploid zygote
- B.diploid zygote
- C.non-motile male gametes
- D.motile male gametes
Show answer
Syngamy is the fusion of a male and a female gamete, and since each gamete is haploid, their union gives a diploid zygote.
Read the full explanation →Human insulin molecule is composed of one α-chain having 21 amino acids and one β-chain having 30 amino acids. How many functional insulin genes occur in adult humans?
- A.One
- B.Two
- C.Three
- D.Four
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Humans have a single functional insulin gene, INS, on the short arm of chromosome 11, and both chains of insulin come from it.
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- A.10⁻⁷ cm
- B.10⁻⁶ cm
- C.10⁻⁴ cm
- D.10⁻³ cm
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Read the full explanation →Which of the following is the general formula for saturated hydrocarbons?
- A.CₙH₂ₙ₊₂
- B.CₙH₂ₙ₋₂
- C.CₙH₂ₙ₊₁
- D.CₙH₂ₙ₋₁
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Read the full explanation →Which one of the following is not an epidemic disease?
- A.Cholera
- B.Malaria
- C.Smallpox
- D.Elephantiasis
Show answer
Elephantiasis, or lymphatic filariasis, is an endemic disease: it stays steadily present in certain regions and develops slowly over years, rather than breaking out suddenly in a large number of people.
Read the full explanation →