Are Elaters Haploid or Diploid?

In Marchantia, some of the sporophytes (spore mother cells) that are diploid will remain diploid and undergo a change to form elaters. The other majority of sporophytes will undergo meiosis and form haploid spores. So, in Marchantia the elaters are diploid. Thus, the correct option is 'B'.

Are elaters multicellular?

These may be single-celled or multi-celled and branched (liverwort elaters can be branched as well) or unbranched.

What do you mean by elaters?

: a plant structure functioning in the dispersal of spores: such as. a : one of the elongated filaments among the spores in the capsule of a liverwort. b : one of the filamentous appendages of the spores in the horsetails.