What is impedance ? When does LCR circuit have minimum impedance?

Explanation

i. The total resistance offered to the flow of current due to resistance R, inductive resistance `X_(1)" and capacitive reacatance "X_(c)` in a circuit is called impedance.
It is given `z=sqrt(R^(2)+(X_(L)-X_(C))^(2))`
ii. At resonance, when `X_(L)=X_(C).`