If $\frac{\text{Path difference}}{\text{Wave length}} = n$ (where $n$ is an integer),what kind of interference is formed?

The figure shows two point sources which emit light of wavelength $\lambda$ in phase with each other and are at a distance $d = 5.5 \lambda$ apart along a line which is perpendicular to a large screen at a distance $L$ from the center of the sources. Assume that $d$ is much less than $L$. Which of the following statement$(s)$ is (are) correct?

Four light waves are represented by:
$(i)$ $y = a_1 \sin \omega t$
(ii) $y = a_2 \sin (\omega t + \phi)$
(iii) $y = a_1 \sin 2\omega t$
(iv) $y = a_2 \sin 2(\omega t + \phi)$
Interference fringes may be observed due to the superposition of:

What is the path difference for destructive interference?

The path difference between two interfering waves at a point on the screen is $171.5$ times the wavelength. If the path difference is $0.01029 \, cm$,find the wavelength in $\mathring{A}$.

The ratio of maximum and minimum intensities in an interference pattern is $36: 1$. The ratio of the amplitude of the two interfering waves will be