Huffman coding makes sure that there is no ambiguity when we decode the bit stream code .so the The variable-length codes assigned to input characters are Prefix Codes, means the codes (bit sequences) are assigned in such a way that the code assigned to one character is not prefix of code assigned to any other character.
so code 1 which is possible ...this follow the prefix property ... ( no prefix is otherone prefix)..
code 2 which is not possible ... bcoz 00 does not follow the prefix property , 0 is code 00 also contain 0 as prefix ,
code 3 it follows prefix property but one of them should be only one bit code ....so its not possible..
I think code2 and code3 are not possible
Code2 = last level of code should be 1 bit. 0 and 1 in the same huffman tree and then 2 bit code 00 not possible.If the tree at the last level ended with 0 , the extended part will be 10 and 11.(See pic)
Code3= not possible as all 2 bit code. As we know last level of code of huffman tree must be 1 bit
In huffman encoding symbols being encoded must be at the leaves of the huffman tree & not in the inner nodes.So code 2 is impossible for sure