Which of the following pairs of elements will not
form ionic compounds?
a. sulfur and oxygen
b. sodium and calcium
c. sodium and sulfur
d. oxygen and chlorine

a. sulfur and oxygen

b. sodium and calcium

d. oxygen and chlorine

Explanation:

The ionic compounds have to be made with element with positive charge(metal) and element with negative charge(gas). Both sulfur and oxygen is gas with negative charge. Both sodium and calcium is metal with positive charge. Chlorine also gas, so it can't make ionic compound with oxygen.

Sodium and sulfur is the only option that can make ionic compound since Sodium is metal and sulfur is gas.

dynamic equilibrium is the answer.