The flame colour produced by potassium compounds is
Correct answer: D. lilac
- A. golden yellow
- B. brick red
- C. apple green
- D. lilac
Explanation
Heating excites the outer electron to a higher level and the colour is emitted as it falls back, the energy gap being characteristic of the element, so potassium gives lilac, sodium golden yellow, calcium brick red and barium apple green. The flame test is the simplest analytical use of atomic emission spectra. Sodium contamination easily masks the potassium colour, so it is viewed through blue glass.
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About Reactions of Group I Elements
Group I elements have one valence electron, so their reactivity increases down the group as ionisation energy decreases. Their reactions with water, oxygen, hydrogen and halogens produce hydroxides, oxides, hydrides and halides, while the behaviour of lithium differs from the heavier metals because of its small ionic size.
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