The correct option is
C A gametophytic free living structure formed in pteridophytes
The gametophyte in Pteridophytes is known as prothallus. It is a small, inconspicuous and multicellular structure which is formed from the germination of haploid spores. It is independent and autotrophic. The prothallus is generally monoecious as it bears both male and female sex organs i.e. antheridia and archegonia respectively or it may be dioecious if male and female sex organs are present on different plants.
So, the correct answer is 'A gametophyte free living structure formed, in pteridophytes'.