Question

If the colour of the flame obtained by performing the flame test of a substance with the help of platinum wire and concentrated \[{\text{HCl}}\] is violet, then the basic radical in the salt is:
A.Barium
B.Potassium
C.Calcium
D.Sodium

Answer 1

Hint: The basic radical present in the salt which gives a violet colour to the flame is a member of the first group of the periodic table. In other words, the odd element is an alkali metal. It has the atomic number 19.

Complete step by step answer:
We know that both alkali metals and their corresponding salts impart some characteristic colours to the flame. This is due to the reason that when an alkali metal element or its salt is put in a flame, its electrons get excited by absorbing the energy from the flame. The electrons of the elements having higher ionization enthalpies get excited to the lower orbits. These electrons fall back from higher to lower energy state and emit radiations of small energy during the process. This corresponds to radiations of lower frequency in the visible region. That is why lithium and sodium, which have high ionization enthalpies impart crimson red and golden yellow colours respectively. On the other hand, the electrons of the elements having lower ionization enthalpies get excited to the higher orbits. These electrons fall back from higher to lower energy state and emit radiations of higher energy during the process. This corresponds to radiations of higher frequency in the visible region. That is why potassium which has low ionization enthalpy imparts a pale violet colour to the flame.
Like alkali metals, alkaline earth metals and their salts also impart characteristic colours to the flame. For example, calcium imparts brick red colour, strontium imparts crimson colour and barium imparts green colour to the flame.

Hence, the correct option is B.

Note:
Among alkaline earth metals, only beryllium and magnesium do not impart any characteristic colour to the flame. This is due to the reason that both beryllium and magnesium have small sizes and very high ionization enthalpies. Hence, the energy of the flame is not sufficient enough to excite the electrons of beryllium and magnesium to higher energy levels. Hence, beryllium and magnesium do not give any colour to the flame.