Applying the Law of Conservation of Momentum, if the final total momentum of 2 objects is 100 kgm/s, what is the initial total momentum?

Ohm's law tells you that i = v/r where v is equivalent voltage and r is equivalent resistance of the circuit
since all circuits have the same voltage, your question is really asking which circuit has the lowest total resistance, since the lower the resistance, the higher the current
circuit a has a resistance of 5 ohms; circuit c is in series so has a resistance of 10 ohms; circuit b is in parallel and therefore has a resistance of 2.5 ohms (review your notes on adding resistances in parallel and series); therefore b has the highest current

Iwould say earthquakes.

Carbon dioxide because it consists of one type of molecule.