what is the difference between "only if" and "if and only if" don't they mean the same thing?

for example, "luke becomes a jedi only if he is trained by yoda". cant you infer that if luke is not trained by yoda then he does not become a jedi from this statement as well as the if and only if statement?

for question 10 why cant we kick up "Any valid moral judgment" ? The statement would be:

if its about a particular action --> formed-consequences