Statement 1: The maximum intensity in interference pattern is four times the intensity due to each slit.

Statement 2: Intensity is directly proportional to square of amplitude.

Let a be the amplitude of waves from each slit. Intensity is directly proportional to square of amplitude i.e., $\mathrm{I}\propto {\mathrm{a}}^2$ Due to each slit ${\mathrm{I}}_1\propto {\mathrm{a}}^2$ 

When destructive interference occurs, then resultant amplitude $=a-a=0$

$\therefore$   Minimum intensity, ${\mathrm{I}}_{min}=0$

When constructive interference occurs, the resultant amplitude = a + a = 2a

$\therefore$    Maximum intensity, ${\mathrm{I}}_{max}\propto (2\mathrm{a}{)}^2$

Hence, ${\mathrm{I}}_{max}\propto 4{\mathrm{a}}^2$

or ${\mathrm{I}}_{max}=4$ times the intensity due to each slit.