Answer:a leech
Explanation: a parasitic relationship is one organism benefit on the other while the other is harmed
c is the answer a benzene
Option (a) is correct.
A reducing agent is the one which loses electrons to other substance.
Here, Zn has oxidation number 0 in the L.H.S of the equation, but on R.H.S its oxidation number is +2 i.e. it Zn has donated two of its electrons to

.
Hence, Zn is the reducing agent here.
12➡6➡3➡1.5
① ② ③
3 half life = 252
half life = 84days