Q.Are Kirchhoff's laws applicable for both AC and DC currents?

[!TLDR] Yes -- both laws are consequences of charge conservation (junction law) and energy conservation (voltage law), which hold at every instant regardless of whether the current is steady …

Kirchhoff's first law is charge conservation applied at a junction, and Kirchhoff's second law is energy conservation applied around a loop; neither of these underlying physical principles cares whether the current happens to be steady (DC) or varying with time (AC) -- charge and energy are conserved at every instant, regardless of the current's time-dependence. So both laws remain valid for AC circuits too, PROVIDED they are applied instantaneously (i.e. treating the instantaneous values of current, resistance/impedance and emf at each moment, rather than assuming steady, unchanging values as in the simple DC examples of this …

Trace both laws back to their underlying conservation principles (charge, energy), which are time-in …

Assuming Kirchhoff's laws are DC-only rules because this chapter's examples all us …