Magnetic Field of Straight Wires question from JEE Main 2022 (30 Jul, Shift 2)

Answer: (c)

1. AB lies on a line through O, so it gives zero field.
2. Three-quarter arc B to C (clockwise): $\frac{3}{4}\cdot\frac{\mu_0 I}{2R} = \frac{\mu_0 I}{4\pi R}\cdot\frac{3\pi}{2}$, into the page.
3. Semi-infinite CD with foot at C, distance $R$: $\frac{\mu_0 I}{4\pi R}$, also into the page.
4. $B = \frac{\mu_0 I}{4\pi R}\left(\frac{3}{2}\pi + 1\right)$
5. So the answer is (c).