when two poles of magnet are bought together regularly it looses it magnet. which process is this called ?

Hysteresis Loss which is the irreversible displacement of the domain wall and irreversible dynamic behavior of the magnetic domain.

The answer is b hope this

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