Determine 2 is an element of that set?

Question

a) {2, {2}}

b) {{2}, {{2}}}

Answer 1

2 is an element of the first set, but not of the second set.  

{2} is a set containing the number 2 as its only element; this set is distinct from the number 2. {{2}} is a set with one element, which is a set.