The question is asking for representation in 5 digits..So prior to finding 10's complement , u have to represent the given number in 5 digits which can be done by appending a 0 to MSB as it does not changes value..
So 5 digit representation of number = (09900)10
So 9's complement of it = (90099)10
So 10's complement of it = (90099)10 + 1
= (90100)10
Hence C) is the correct answer..