Let S={∅,{∅}}S = \{\emptyset, \{\emptyset\}\}S={∅,{∅}} be a set. Which of the following is NOT an element of the power set P(S)\mathcal{P}(S)P(S)?
∅\emptyset∅
{∅}\{\emptyset\}{∅}
{{∅}}\{\{\emptyset\}\}{{∅}}
{{{∅}}}\{\{\{\emptyset\}\}\}{{{∅}}}