The correct answer is: A. Reduce
When one leg of a parallel circuit is opened out, the total current will reduce. This is because the total resistance of the circuit will increase, which will cause the current to decrease.
The total resistance of a parallel circuit is equal to the reciprocal of the sum of the reciprocals of the individual resistances. When one leg of the circuit is opened out, the resistance of the circuit will increase. This is because the total resistance of a parallel circuit is inversely proportional to the number of branches in the circuit. When one branch is removed, the number of branches in the circuit decreases, which causes the total resistance to increase.
The increase in resistance will cause the current to decrease. This is because the current in a parallel circuit is inversely proportional to the resistance. When the resistance increases, the current will decrease.
Therefore, when one leg of a parallel circuit is opened out, the total current will reduce.