What are some of the problems with using flame tests as a way to identify substances?

Different substances can produce similar results in color. This can cause uncertainty with identifying the substance.

Mg-26 and mg-24 are pair of isotopes. isotopes are defined as atoms of the same element having same atomic number but different mass number. i hope that was .

Density= mass/volume so 5.1 divided by 4.7 is  5.1 / 4.7 =1.08510638298round to the correct number of sig figs