Give two reasons why the flame test is sometimes invalid

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.

Just took the quiz on edgenuity and the correct answer is "c.  4.54 x  10–12  j"