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Question 7 from the 2015 Australian Chemistry Olympiad was:

Which list below gives non-metals that can be found in their elemental form in nature?

(a) neon, phosphorus, fluorine
(b) helium, hydrogen, iodine
(c) helium, carbon, fluorine
(d) nitrogen, chlorine, sulfur
(e) oxygen, chlorine, phosphorus

I was somewhat confused when all the options included reactive elements such as sulfur, phosphorus and the halogens. I know neon is a noble gas and is present in minute quantities in the atmosphere, and nitrogen and oxygen gases are present as diatomics.

However, where are hydrogen, phosphorus, sulfur, fluorine, chlorine and iodine found in their elemental forms in nature? (Answer is B)

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    $\begingroup$ It is not a particularly easy question. But some examples should be more obvious than others. Native sulphur is found in some volcanos; a large part of the solar system is made of hydrogen. And the least reactive halogen is iodine. I'd have guessed 2 by elimination. $\endgroup$ – matt_black Apr 1 '18 at 13:24
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I agree with Matt Black's comment on the question. The question is rather tricky and the answer can only be determined by the process of elimination.

  1. Have to assume we're talking about STP.
  2. "In nature" is ambiguous, so assume the question means "on earth."
  3. It is also somewhat ambiguous what "elemental form" means. Assume that it means that element is only combined with itself since only the noble gases exist as monoatomic species.

The noble gases (helium and neon) and exist as monoatomic gasses at STP and can be found in the atmosphere.

Oxygen and nitrogen are diatomic gases and both exist in earth's atmosphere.

Sulfur is found in volcanic vents.

Carbon is found both as graphite and diamonds on the earth.

So, the list becomes:

  1. neon, phosphorus, fluorine
  2. helium, hydrogen, iodine
  3. helium, carbon, fluorine
  4. nitrogen, chlorine, sulfur
  5. oxygen, chlorine, phosphorus

Oxygen is ubiquitous on earth and phosphorus is so reactive with oxygen that elemental phosphorous just won't be found on earth. However, elemental phosphorous might be found on the moon for example.

  1. neon, phosphorus, fluorine
  2. helium, hydrogen, iodine
  3. helium, carbon, fluorine
  4. nitrogen, chlorine, sulfur
  5. oxygen, chlorine, phosphorus

So now we are left with the halogens -- fluorine, chlorine, and iodine. Iodine is the least reactive, so "elemental iodine" is the most probable to be found in nature.

Thus the answer must be #2. However this is really an "educated guess," not a "fact" since the question is so ambiguous.

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According to Volcanic emissions of molecular chlorine Geophysical Research Abstracts Vol. 14, EGU2012-12386:

When eruption ceases, the cooling volcanic cone can work as a giant chemical reactor to convert residual HCl into molecular chlorine (Cl2). Up to 60 ppmv (180 mg/m3) of Cl2 together with 30-77 ppmv HCl were measured in gas emissions from the Tolbachik scoria cones, Kamchatka, which are still hot after the 1975-1976 eruption.

...

The estimated total discharge of Cl2 from the Tolbachik cones is ca. 12-16 t/yr.

There is also a corresponding full paper in Geochimica et Cosmochimica Acta Volume 87, 15 June 2012, Pages 210-226.

So, although the Olympiad wanted you to answer "b", the above necessitates that "d" is a correct answer.

Note also that there was a highly similar, but more sensible, question (#7), in the 2014 U.S. NATIONAL CHEMISTRY OLYMPIAD:

Which list gives nonmetals that are found in their elemental forms in nature?

(A) neon, phosphorus, fluorine
(B) helium, hydrogen, iodine
(C) nitrogen, oxygen, sulfur
(D) oxygen, chlorine, phosphorus

with "(C)" being correct.

Here, the American Chemical Society is on record indicating "(B) helium, hydrogen, iodine" is incorrect, directly contradicting the Australians.

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Halogenes usually do not occur in their elemental state in nature.

However, under certain circumstances there are exceptions from this rule.

E.g.

  • Fluorine ($\ce{F2}$) exists in calcium fluorite (antozonite) that has been exposed to radioactive radiation.

  • Bromine ($\ce{Br2}$) can occur in atmospheric plumes of degassing volcanoes.

  • Iodine ($\ce{I2}$) is produced by some kelp in response to oxidative stress.

Chlorine ($\ce{Cl2}$) is also said to occur in volcanic gases, but I could not find a reference that supports this claim.

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Iodine is volatilized from the sea as methyliodide, elemental iodine, and possibly other inorganic compounds...

Reference

Thus iodine is naturally occurring as the element. That settles the original question.

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hydrogen, phosphorus, sulphur, fluorine, chlorine and iodine will exist in their elemental states, as this simply means that they aren't bonded to any other element; their structure is only formed from that particular element. this means that they ill exist as H2,P4, S8, F2, Cl2 and I2.

but the answer is two as we typically won't find fluorine, chlorine and phosphorus as their elemental molecules in nature as they are too reactive.

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