A double slit setup is shown in the figure. One of the slits is in medium $2$ of refractive index $n_2$. The other slit is at the interface of this medium with another medium $1$ of refractive index $n_1\left(\ne n_2\right)$. The line joining the slits is perpendicular to the interface and the distance between the slits is $d$. The slit widths are much smaller than $d$. A monochromatic parallel beam of light is incident on the slits from medium $1$. A detector is placed in medium $2$ at a large distance from the slits, and at an angle $\theta$ from the line joining them, so that $\theta$ equals the angle of refraction of the beam. Consider two approximately parallel rays from the slits received by the detector.
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Which of the following statement(s) is(are) correct?

1. A The phase difference between the two rays is independent of $d$.
2. B The two rays interfere constructively at the detector.
3. C The phase difference between the two rays depends on $n_1$ but is independent of $n_2$
4. D The phase difference between the two rays vanishes only for certain values of d and the angle of incidence of the beam, with  \(\theta\) being the corresponding angle of refraction.