Which of the following are the most favourable conditions for liquefying a gas ?
- A.Low pressure and high temperature
- B.Low pressure and low temperature
- C.High pressure and high temperature
- D.High pressure and low temperature
Correct answer
Explanation
The correct answer is D, High pressure and low temperature. High pressure pushes the gas molecules close together and low temperature slows them down, so the attractive forces can hold them as a liquid.
In a gas the molecules move fast and are far apart. Compressing the gas reduces the space between them, and cooling it takes away the kinetic energy that lets them escape one another. A gas can be liquefied by pressure only if it is first cooled below its critical temperature; above that temperature no pressure, however high, will turn it into a liquid. This is why LPG is stored as a liquid under pressure in cylinders, and why oxygen and nitrogen are liquefied by deep cooling and compression.
A is wrong: low pressure and high temperature keep molecules far apart and fast, the opposite of what is needed.
B is wrong: cooling helps, but at low pressure the molecules stay too far apart.
C is wrong: at high temperature the molecules move too fast to settle into a liquid.
Exam tip: liquefy a gas with high pressure plus a temperature below its critical temperature.
Practice Questions
View allSyngamy results in formation of
- 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
Show answer
Humans have a single functional insulin gene, INS, on the short arm of chromosome 11, and both chains of insulin come from it.
Read the full explanation →Which one of the following is the value of one nanometer?
- A.10⁻⁷ cm
- B.10⁻⁶ cm
- C.10⁻⁴ cm
- D.10⁻³ cm
Show answer
One nanometre is 10⁻⁹ metre, and since one metre is 100 (10²) centimetres, it equals 10⁻⁷ centimetre. The prefix nano means one billionth.
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
Show answer
Saturated open-chain hydrocarbons are the alkanes, and every alkane fits the formula CₙH₂ₙ₊₂. In a saturated hydrocarbon every carbon atom is joined to others only by single bonds, so each carbon holds the largest possible number of hydrogen atoms.
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 →