When a thin layer of alcohol (nalcohol = 1.39) is poured over a glass plate (nglass = 1.52), reflected monochromatic light from the plate is enhanced when = 640 nm and eliminated when = 512 nm. Determine the minimum possible thickness of the alcohol layer such that the above conditions are simultaneously met. Assume that nair = 1.0 and that the light is incident perpendicular to the plate.

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

The chemical reactions lab we did is typically called a "copper plating lab,  because the acid solution cleaned the pennies and made the copper look shinier;   the acid solution cleaned the paperclips and made them look like pennies;   &   the copper from the pennies was removed, and then added to the paperclips.