Which of the following characteristics is common to hydrogen, nitrogen, oxygen and carbon dioxide?
- A.They are all diatomic.
- B.They are all gases at room temperature.
- C.They are all coloured.
- D.They all have same reactivity.
Correct answer
Explanation
The correct answer is B, They are all gases at room temperature. Hydrogen, nitrogen, oxygen and carbon dioxide all exist as gases at about 25 °C and normal atmospheric pressure.
Hydrogen boils at about −253 °C, nitrogen at −196 °C and oxygen at −183 °C, so all three are gases at room temperature. Carbon dioxide does not even have a liquid phase at normal pressure: solid carbon dioxide, called dry ice, turns directly into gas at −78.5 °C. Nitrogen and oxygen together make up about 99 per cent of dry air, and carbon dioxide is a trace gas in it.
A is wrong: H2, N2 and O2 are diatomic, but carbon dioxide (CO2) has three atoms, so it is triatomic.
C is wrong: all four gases are colourless.
D is wrong: their reactivity differs widely; nitrogen is almost inert because of its strong triple bond, oxygen supports combustion, hydrogen burns readily, and carbon dioxide puts out fire.
Exam tip: atomicity — H2, N2, O2 diatomic; CO2 and O3 triatomic; noble gases monatomic. Dry ice sublimes at −78.5 °C.
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 →