Why zero group element do not form compound under ordinary conditions?

Why do the Gr-18 elements not form compounds under ordinary conditions ?

Why zero group elements are inert ?

Why zero group elements do not form diatomic molecules ?

Many thermodynamically feasible reactions do not occur under ordinary conditions. Why ?

Two elements X and Y combine to form a compound XY. Under what conditions the bond formed between them will be ionic ?

Explain why cis and trans isomers do not change into one another under ordinary conditions?

Justify the following statements : Many thermodynamically feasible reactions do not occur under ordinary conditions.