Question

Give two reasons why the flame test is sometimes invalid

Answer 1

Answer: 1.A false positive and 2.A false negative.

Explanation:

A false positive the classic example is the contamination of almost any sample with sodium ions which gives an intense yellow line even when the sodium is present as only impurity.

A false negative here sodium ions is the culprit that masks other emissions unless the emissions are resolved spectroscopically rather than simply visually.

Answer 2

The two reason behind the invalidity of flame test are false positive and false negative.
while performing the flame test you must have to be accurate otherwise you will get false results may be positive for some element or may be negative in case the element is present. The main reason to get the false positive and false negative is the presence and contamination of sodium.