In a Young's double slit experiment, the distance between the two identical slits is 6.1 times larger than the slit width. Then the number of intensity maxima observed within the central maximum of the single slit diffraction pattern is :

In diffraction, angular width of central maxima is 2λ/b where b is slit width.
In Young's double slit experiment, angular width of each fringe is λ/d where d is the distance between the two slits.
Given : d=6.1b
So, number of maximas observed in central maxima of diffraction pattern
n = (2λ/b) / (λ/d)
∴ n = 2d/b = 2 × 6.1 = 12.2
Thus 12 maximas are observed.