Question

The metal which gives brick red colour in flame test is:
A.Barium
B.Calcium
C.Strontium
D.Radium

Answer 1

Hint: The elements of s-block, i.e., the members of alkali metal and alkaline earth metal groups are known to impart characteristic colours to the flame. The metal which gives brick red colour has the atomic number 20.

Complete step by step answer:
Just like alkali metals, when an alkaline earth element or its salt is put in a flame, its electrons get excited by absorbing energy from the flame. The electrons of elements having higher ionization energies get excited to the lower orbit. These electrons while falling back from higher energy state to lower energy state, emit radiations of lower frequency in the visible region. This is responsible for the characteristic colour. Whereas, the electrons of elements with low ionization energies get excited to higher orbits and while falling back, they emit radiations of high energy in the visible region. Barium, calcium, strontium, radium all belong to alkaline earth metals group. When barium or a salt of barium is put in a flame, it imparts a characteristic green colour to the flame. Similarly, calcium imparts characteristic brick red colour, strontium imparts crimson red colour and radium imparts crimson colour.
Thus, calcium which has atomic number 20 gives brick red colour in flame test.

So, the correct answer is option B.

Note: Beryllium and magnesium are the only alkaline earth metals which do not give any colour in flame test.
This is because they have small size and very high ionization enthalpies and so the energy of the flame is not sufficient enough to excite the electrons to higher energy levels. Hence, they do not impart any colour to the flame.