The ion that has the same e- arrangement as ar:

a k+
b cl-
c s2-
d ca2+
e all of these

the answer is E- all of these

to check if these ions have the same e- configuration, check them in the periodic table and see where they land when you take or add electrons. 

for example, K is one space away to be like Ar, which is just one space behind. having a positive charge +1, means that it has one less electron. if you remove this electron, it is like Ar because is one space.

another example-> S-2  means you have add two electrons because charge is negative, so you add. two spaces after S land in Ar. so it is same e- configuration as Ar.

Elias is almost correct. he just got it backwards.the correct answer is that it demonstrates elastic potential energy transforming into kinetic energy.