What is represented by the $P$-wave in an $ECG$?

Consider the following statements with respect to $ECG$ [Electrocardiogram] and choose the correct answer.
Statement $I$ : '$P$' wave represents the depolarisation of ventricles.
Statement $II$ : '$T$' wave represents the repolarisation of ventricles.

Match the Column $-I$ with Column $-II$.

Column $-I$	Column $-II$
$(a) \; P-$wave	$(i) \; \text{Depolarisation of ventricles}$
$(b) \; QRS$ complex	$(ii) \; \text{Repolarisation of ventricles}$
$(c) \; T-$wave	$(iii) \; \text{Coronary ischemia}$
$(d) \; \text{Reduction in the size of } T-$wave	$(iv) \; \text{Depolarisation of atria}$
	$(v) \; \text{Repolarisation of atria}$

Select the correct option:
$(a) \quad (b) \quad (c) \quad (d)$

Which wave of the human heart $ECG$ $(PQRST)$ is used for determining the heart rate of an individual?

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

$X-$ In $ECG,$ $P-$ wave represents the electrical excitation of the ventricle.
$Y -$ $QRS$ waves represent depolarization of atria.