what is the technique for testing different chemicals known as ? it says that when they were burnt, they gave off a different colour ... so what is that technique known as ?

A flame test is an analytical procedure used in chemistry to detect the presence of certain elements, primarily metal ions, based on each element's characteristic emission spectrum. The color of flames in general also depends on temperature; see flame color.

Explanation:

I hope it's help u ;)

3 hours because it is a decent distance.

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.