Which physical quantity is there in $A.C.$ circuit as displacement variable?

In an oscillating $LC$-circuit,$L = 3 \ mH$ and $C = 2.7 \ \mu F$. At $t = 0$,the charge on the capacitor is zero and the current is $2 \ A$. The maximum charge that will appear on the capacitor will be

The magnetic energy in an inductor changes from maximum value to minimum value in $5 \ ms$. When connected to an $A.C.$ source,the frequency of the source is (in $Hz$)

$A$ charged $30\; \mu F$ capacitor is connected to a $27\; mH$ inductor. What is the angular frequency of free oscillations of the circuit?

The natural frequency of an $L-C$ circuit is $1,25,000 \text{ cycle/s}$. Then the capacitor $C$ is replaced by another capacitor with a dielectric medium of dielectric constant $K$. In this case,the frequency decreases by $25 \text{ kHz}$. The value of $K$ is

If maximum energy is stored in the capacitor at $t = 0$,find the time after which the current in the circuit will be maximum. Given $L = 25 \, mH$ and $C = 10 \, \mu F$.