The answer can be explained when you burn something cleanly (with a very hot item) or not. With a candle lots of Carbon dioxide is producted but when using a bunson burner hardly any CO2 is produced.
So potassium is more reactive than lithium because the outer electron of a potassium atom is further from its nucleus than the outer electron of a lithium atom. Hope this answers the question. Have a nice day. Feel free to ask more questions.
Lets find the electronegativity difference between the bonded atoms;
C-H = 2.6-2.2 = 0.4
C-F = 4.0-2.6 = 1.4
F-F = 4.0-4.0 = 0
H-O = 3.4-2.2 = 1.2
Here the electronegativity difference is highest for C-F bond hence C-F bond is most polar.
Amplitude is the awnser glad I could help you
