Where is the pacemaker located?

The correct structure of the drug paracetamol is:

Consider the following reactions:
$C_2H_2 \xrightarrow[500^{\circ}C]{\text{red hot iron tube}} A$
$A \xrightarrow[70^{\circ}C]{\text{conc. } HNO_3, \text{conc. } H_2SO_4} B$
$B \xrightarrow{LiAlH_4} C_6H_5-N=N-C_6H_5$
$A$ and $B$ are:

If $u=e^{x^2-y^2}$,then

The correct curve between the magnetic induction $(B)$ along the axis of a long solenoid due to current flow $i$ in it and distance $x$ from one end is:

The radius of the circle $r = \sqrt{3} \sin \theta + \cos \theta$ is