In all the leads of $ECG$,all following are positive waves except

Arrange and select the following events in the correct sequence during the measurement of blood pressure by a sphygmomanometer.
$i.$ Pulsatile sound disappears.
$ii.$ Cuff is inflated to block the brachial artery by external pressure.
$iii.$ First pulsatile sound is heard indicating systolic pressure.
$iv.$ Pressure in the cuff is slowly lowered.
$v.$ Cuff is wrapped tightly around the upper arm.

In $ECG,$ $T$-wave represents:

Given below is the $ECG$ of a normal human. Which one of its components is correctly interpreted below?

Complete the missing words in the statements given below:
$(a)$ Plasma without clotting factors is called serum.
$(b)$ $.........$ and monocytes are phagocytic cells.
$(c)$ Eosinophils are associated with $.........$ reactions.
$(d)$ $.........$ ions play a significant role in clotting.
$(e)$ One can determine the heart beat rate by counting the number of $.........$ in an $ECG$.

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