What is the reason we prefer $A.C.$ voltage over $D.C.$ voltage for power transmission?

In an $LCR$ series circuit,when $L$ is removed from the circuit,the phase difference between voltage and current is $\frac{\pi}{3}$. If $C$ is removed from the circuit instead of $L$,the phase difference is again $\frac{\pi}{3}$. The power factor of the circuit is $(\tan 60^{\circ}=\sqrt{3})$.

Three alternating voltage sources $V_1 = 3 \sin \omega t \text{ V}$,$V_2 = 5 \sin(\omega t + \phi_1) \text{ V}$,and $V_3 = 5 \sin(\omega t - \phi_2) \text{ V}$ are connected in series with a resistor $R = \sqrt{\frac{7}{3}} \, \Omega$ as shown in the figure (where $\phi_1 = 30^\circ$ and $\phi_2 = 127^\circ$). Find the peak current (in Ampere) through the resistor.

Answer the following questions:
$(a)$ In any $ac$ circuit, is the applied instantaneous voltage equal to the algebraic sum of the instantaneous voltages across the series elements of the circuit? Is the same true for $rms$ voltage?
$(b)$ Why is a capacitor used in the primary circuit of an induction coil?
$(c)$ An applied voltage signal consists of a superposition of a $dc$ voltage and an $ac$ voltage of high frequency. The circuit consists of an inductor and a capacitor in series. Show that the $dc$ signal will appear across $C$ and the $ac$ signal across $L$.
$(d)$ $A$ choke coil in series with a lamp is connected to a $dc$ line. The lamp is seen to shine brightly. Insertion of an iron core in the choke causes no change in the lamp's brightness. Predict the corresponding observations if the connection is to an $ac$ line.
$(e)$ Why is a choke coil needed in the use of fluorescent tubes with $ac$ mains? Why can we not use an ordinary resistor instead of the choke coil?

The figure shows a system of an inductor and a parallel plate capacitor made of $2$ parallel circular plates of area $A$,filled with a dielectric liquid of dielectric constant $K$. $A$ small leak develops in the capacitor,and the liquid starts to fill the inductor of the same dimensions having $n$ turns per unit length. Find the ratio of the magnitude of the initial reactance to the final reactance of the circuit after the liquid fills the inductor completely.
Given: $\omega^2 A^2 n^2 = c^2$
$\omega \rightarrow$ angular frequency of $AC$
$c \rightarrow$ speed of light
$\mu_r \rightarrow$ relative permeability of the liquid

The $i -
u$ curve for an anti-resonant circuit is: