Question

A salt burns with apple green flame is:
A.Sodium chloride
B.Potassium nitrate
C.Magnesium carbonate
D.Barium chloride

Answer 1

Hint:Try to recall the lab experiment involving flame test, in order to answer this question.
We will follow the colour of flame as a clue, then try to find which of these given options impart apple green colour to the flame.

Complete step by step answer:
We will use the knowledge of flame test to answer this question because flame test is applicable only in case of metal ions and all the options given in the question are metals.
A flame test is an analytical process which is used in the field of chemistry in order to detect the presence of some specific elements, primarily metal ions, based on the characteristic of each element's emission spectrum. The colour of flames in general also is dependent on the temperature in which the experiment is carried out.
The test involves introduction of a small sample of the element to a hot, non-luminous flame, and detecting the colour of the resulting flame. The idea of this test is that the sample atoms evaporate and since they are in a high temperature, they emit light when being in flame. Sample in bulk emits light too, but the light emitted is not good for analysis. Bulk samples emit light mainly due to the motion of the electrons, therefore it has a broad spectrum, consisting of a wide range of colours. Distinct atoms of a sample existing in the flame can emit colour, only due to the electronic transitions between various atomic energy levels. Those transitions emit light of very certain frequencies. Therefore, the flame acquires the colour, which is mainly determined by properties of the shells of atomic energy of the chemical element, of the substance which is being put into the flame. The flame test is a relatively easy experiment to set up and hence it is often demonstrated or carried out in chemistry classes in schools.
So the correct answer is barium chloride.


Note:
Other elements which impart colour to the flame are, arsenic which gives blue colour, boron gives bright green, beryllium white, and calcium brick red etc.
In the labs, we usually make a paste of the compound under consideration, with conc. Hydrochloric acid and then with the help of a glass rod, we do the flame test.