Which one of the following pairs do not impart colour to the flame?
A
BeCl2 and SrCl2
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B
BeCl2 and MgCl2
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C
CaCl2 and BaCl2
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D
BaCl2 and SrCl2
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Solution
The correct option is BBeCl2 and MgCl2
On heating an alkali earth metal or its salt, the electrons are excited easily to higher energy levels because of absorption of energy. When these electrons return to their ground states, they emit extra energy in form of radiations which fall in the visible region thereby imparting a characteristic colour to the flame.
Be and Mg do not impart any colour to the flame i.e. they do not give flame test. This is due to their very small size. Ca, Sr and Ba impart brick red, Blood red and Apple green colours respectively to the flame.