Question

Which of the following metals will give an apple green colour on the Busen flame?
(A) $Ba$
(B) $Sr$
(C) $Ca$
(D) $K$

Answer 1

Hint: All the given compounds are the alkaline earth metals. These are so named as the hydroxides and oxides of these metals are alkaline in nature. These metals are found in the earth’s crust. These are highly reactive in nature. The alkaline earth metals have low ionisation energy, low electron affinity, and low electronegativity. These are good conductors of electricity.

Complete Step by Step Answer:
When the salts of these metals are heated on a bunsen flame, then they decompose thermally and give different colours. A colour is imparted to the flame when the salts of these metals are heated because of the movement of valence electrons from a lower energy level to a higher energy level of metal ion. When the electron comes back to its original energy level, it emits some energy in the form of light whose wavelength matches any light in the visible region. $Ba$ metal will give an apple green colour on Bunsen flame.
Hence, the correct answer is Option: (A)$Ba$.

Note: Other metals like calcium exhibit a brick red colour, strontium exhibits a crimson colour and potassium imparts a lavender colour. However, beryllium and magnesium do not impart any colour to the flame. This is because of the small size of these metals. Also, the solubility of the hydroxides of these metals is different for different metals. $Be{{(OH)}_{2}}$ and $Mg{{(OH)}_{2}}$ are almost insoluble, $Ca{{(OH)}_{2}}$ is sparingly soluble while $Sr{{(OH)}_{2}}$ and $Ba{{(OH)}_{2}}$ are fairly soluble.