The Q-factor of a parallel tuned circuit refers to the quality factor, which is a measure of the efficiency of the circuit in storing and transferring energy. A higher Q-factor indicates a more efficient circuit.

The Q-factor of a parallel tuned circuit can be increased by decreasing the circuit resistance. This is because the Q-factor is determined by the ratio of reactance to resistance in the circuit.

When the circuit resistance is decreased, the reactance becomes more dominant in the circuit. Reactance is the opposition to the flow of alternating current caused by inductance and capacitance.

Here's a detailed explanation of why decreasing circuit resistance increases the Q-factor:

1. Definition of Q-factor:
The Q-factor of a circuit is defined as the ratio of the reactance to the resistance.
Q = X/R
Where X is the reactance and R is the resistance.

2. Reactance in a parallel tuned circuit:
In a parallel tuned circuit, the reactance is mainly due to the inductance and capacitance. The reactance can be calculated using the following formulas:
XL = 2πfL - Inductive reactance
XC = 1/(2πfC) - Capacitive reactance
Where f is the frequency, L is the inductance, and C is the capacitance.

3. Relationship between reactance and resistance:
In a parallel tuned circuit, the total impedance is the reciprocal of the sum of the reciprocals of the reactance and resistance.
1/Z = 1/X + 1/R
As the resistance decreases, the total impedance decreases, which means the reactance becomes more dominant in the circuit.

4. Relationship between Q-factor and reactance:
Since the Q-factor is the ratio of reactance to resistance, when the resistance decreases, the Q-factor increases.
Q = X/R
As the reactance becomes more dominant in the circuit due to decreased resistance, the Q-factor increases.

Therefore, the correct answer is option 'B' - decreasing circuit resistance. By decreasing the circuit resistance, the Q-factor of a parallel tuned circuit can be increased, resulting in a more efficient circuit in terms of storing and transferring energy.