How can the rate of heart beating be obtained?

The given diagram represents a normal $ECG$ record of a human heart. Select the $CORRECT$ match from the options given below:

Given below are two statements.
Statement $I$ - Graphical recording of electrical variations detected at the surface of body during their propagation through the wall of heart is electrocardiograph.
Statement $II$ - The instrument used for the graphical recording of electrical variations detected at the surface of body during their propagation through wall of heart is electrocardiogram.
In the light of above statements,select the correct option given below:

Which wave is produced when the action potential is conducted from the $AV$ node to the Purkinje fibers?

The $QRS$ complex in a standard $ECG$ represents:

The diagram given here is the standard $ECG$ of a normal person. The $P$-wave represents the