Let L={0,10,110,1111} . this language satisfies the prefix property since a string in this language will not act as prefix for other strings in this language. Consider another language L1={01,11,110,011}. In this language 01 is acting as a prefix for 011 and 11 is acting as a prefix for 110. Therefore this is not a language satisfying prefix property.
Just have a look at option d.
Language contains strings over (0+1)* where number of 0's = number of 1's
consider 2 strings 01,0110 in the language. 01 is a prefix for 0110. So this language does not satisfy prefix property.
Other three languages satisfy prefix property.
