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My question to ask is "Does $\ce{Fe^2+}$ ion give flame test?"

Background: Last month, I gave the JEE exam and a question was as follow:

Number of metal ions characterized by flame test among the following is ___:

$\ce{Sr^2+,Ba^2+,Ca^2+,Cu^2+,Zn^2+,Co^2+,Fe^2+}$

The answer provided by them was 4 which I'm sure is incorrect considering they only considered the first 4 ions given in the list but the answer should be 5 or 6

A videographic/reputed source would be appreciated.

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Zinc, cobalt and iron salts do not give a color to the flame, whatever the method used, and whatever the chosen salt. Try to do it yourself ! It is easy. Anybody can do it. You may see a yellow color in the flame. It is due to some sodium impurities, because the test for sodium is extremely sensitive. It is positive even with trace amounts of sodium compounds. Looking at the flame with a spectroscope may help you be convinced that the yellow color is the famous Na D line (and even a double line, sometimes difficult to show that it is double)

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  • $\begingroup$ They do give a color in flame test: en.wikipedia.org/wiki/Flame_test. Can you kindly explain from where does the sodium impurity comes from? $\endgroup$ Feb 13 at 4:57
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    $\begingroup$ @Nilay Ghosh. I have read the wikipedia reference. They say that all elements produce a flame test. I would be pleased to see how they have seen for example zinc producing a flame. Under which conditions ? And what is its spectrum ? With a usual Bunsen flame, zinc does not produce a colored flame. Try if you doubt. Furthermore this wikipedia text has mistakes. For example, they state that the violet potassium flame is invisible through cobalt glass. It is wrong. But it is true for the yellow sodium line. Sodium is not potassium. $\endgroup$
    – Maurice
    Feb 13 at 9:01
  • $\begingroup$ @Nilay Ghosh. All substances have one or two ppm of some sodium impurity. $\endgroup$
    – Maurice
    Feb 13 at 9:04

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