b
The condition for maxima in Young's double slit experiment is \(d \sin \theta=n \lambda\) where \(d\) is the separation between the slits and \(\lambda\) is the wavelength of light used.

The maxima that is farthest from the slits is infinitely up or infinitely down the screen and corresponds to \(\theta=\frac{\pi}{2}\).

So, with the given condition, we have, \(n =\frac{ d \sin \left(90^{\circ}\right)}{\lambda}=\frac{ d }{\lambda}=2\)

Thus, we have two maxima on the screen on either side of the central maxima. Thus, the maximum number of possible maxima observed are \(2+1+2=5\).