The atomic number of Re is 75. The atomic mass of one of its isotopes is 186. How many electrons are in this particular isotope.

75 electrons

Explanation:

Since there is no charge, electrons and protons are the same number. Atomic numbers indicate the amount of protons.

organisms that lack symmetry are called asymmetrical and belong to phylum porifera/sponges.

organisms with specialized stinging cells belong to phylum cnidaria. stinging cells are called cnidoblast cells.

cnidarians show two morphological forms : polyp (sessile) and medusa (mobile)

filter feeding is observed in porifera members.  

alternation of generation is observed in coelenterata or cnidaria. there is alternation of asexual polyp form and sexual medusoid form. it is also referred as metagenesis.

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.