What is the $Q$-factor (Quality factor) and on what factors does it depend?

Which of the following combinations should be selected for better tuning of an $L-C-R$ circuit used for communication?

$A$ sinusoidal voltage having a maximum value of $283 \ V$ and a frequency of $50 \ Hz$ is applied to an $LCR$ series circuit where $R = 3 \ \Omega$,$L = 25.48 \ mH$,and $C = 796 \ \mu F$. What is the impedance at resonance condition (in $\Omega$)?

$A$ capacitor of $250\,\mu F$ is connected in parallel to a coil of inductance $0.16\,mH$, while its effective resistance is $20\,\Omega$. Determine the resonant frequency.

$A$ series $LCR$ circuit containing $5.0 \, H$ inductor,$80 \, \mu F$ capacitor,and $40 \, \Omega$ resistor is connected to a $230 \, V$ variable frequency $AC$ source. The angular frequencies of the source at which the power transferred to the circuit is half the power at the resonant angular frequency are likely to be:

$A$ $10 \, \Omega$ resistor, a $5 \, \text{mH}$ inductor, and a $10 \, \mu\text{F}$ capacitor are connected in series. When a suitable frequency alternating current source is connected to this combination, the circuit resonates. If the resistance is halved, the resonance frequency: