Question

An ion which imparts lilac colour to the flame and purple red through blue glass is:
A)sodium
B)chlorine
C)calcium
D)potassium

Answer 1

Hint: An ion that has 18 electrons and 19 neutrons. When it is exposed to heat or flame, it imparts a lilac(violet ) colour.

Complete step-by-step answer:
-The alkali metals and their salts impart characteristic colour to an oxidising flame. This is because the heat from the flame excites the outermost orbital electron to a higher energy level. When the electron comes back to the ground state after excitation, there is an emission of radiation in the visible region.
-This is why the flame also changes colour according to the light emitted by the ion.
-Discussing option A, sodium loses one electron and becomes a cation. This produces yellow colour when exposed to flame.
-Discussing option B, chlorine gains one electron and becomes an anion. This produces green colour when exposed to flame.
-Discussing option C, calcium loses two electrons and becomes a cation. This produces brick red colour when exposed to flame.
-Discussing option D, potassium loses one electron and becomes a cation. This produces lilac colour when exposed to flame.
Through blue glass, potassium gives purple-red color.

Clearly, the answer is D.

Note: The flame test does give us information about the ion but it is not quantitative data. Sometimes, the impurities present in sodium present in the molecules, can give us pale yellow only through blue glass.