Diffraction of light at a single slit, the pattern obtained consists of a central bright band having alternate dark and weak bands of decreasing intensity on both sides
For nth minima (secondary),
$\sin\, \theta_{n}=\frac{n \lambda}{a}$
For $nth$ maxima (secondary),
$\sin\, \theta_{n}=\left(2n+1\right) \frac{\lambda}{2a}$
Thus, point 5 corresponds to path difference of extreme rays equal to $2\lambda$.
