c
(c) Magnetic field at any point lying on the current carrying straight conductor is zero.
Here $H_1$ = Magnetic field at $M$ due to current in $PQ$.
$H_2$ = Magnetic field at $M$ due to $QR$ + magnetic field at $M$ due to $QS$ + magnetic field at $M$ due to $PQ$
$ = 0 + \frac{{{H_1}}}{2} + {H_1} = \frac{3}{2}{H_1}$
$==>$$\frac{{{H_1}}}{{{H_2}}} = \frac{2}{3}$