how many days does it take a perfect black body cube of 0.01m on a side at 30degree to radiate the same amount of energy that 100watts light bulb uses in one hour​

When someone eats food

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

Carbon dioxide because it consists of one type of molecule.