Put the pairs of atoms in order, with the pair that has the biggest electronegativity difference between the two atoms at the top of your list. Phosphorus and lithium Chlorine and cesium Aluminum and oxygen Bromine and bromine Oxygen and strontium

Below are the electronegativties and the differences between the given values in order to arrive to the final answer.

(1) phosphorus: 2.19 lithium: 0.98; difference = 1.21

(2) chlorine: 3.16 cesium: 1.12; difference = 2.04

(3) aluminum: 1.61 oxygen: 3.44; difference = 1.83

(4) bromine: 2.96 bromine: 2.96; difference = 0

(5) oxygen: 3.44 strontium: 0.95; difference = 2.49

Therefore, the order of electronegativity difference from biggest to least is 5, 2, 3, 1, and 4