b
(b) For maximum intensity on the screen
\(d\sin \theta = n\lambda \Rightarrow \sin \theta = \frac{{n\lambda }}{d} = \frac{{n(2000)}}{{7000}} = \frac{n}{{3.5}}\)
Since maximum value of \(\sin \theta \) is \(1\)
So \(n = 0,\,\,1,\,\,2,\,\,3,\) only. Thus only seven maximas can be obtained on both sides of the screen.