Answer:
S1
Step-by-step explanation:
Has to be S1. This is pretty glaring to me. It's said from the question that the chemical reaction that took place is given by the following
S1 + G = S2, with S2 being an offspring of the first S1. When S1 got reacted, it broke down into S2, so, this only confirms that both S1 and E2 are S3 are compounds.