The correct statement is option 1: The Earth`s crust is brittle in nature.

Option 1: This statement is correct. The Earth`s crust, which is the outermost layer of the Earth, is indeed brittle in nature. It is composed of solid rocks that can fracture and break when subjected to stress.

Option 2: This statement is incorrect. The mean thickness of the oceanic crust is around 7 km, while the mean thickness of the continental crust is around 35 km. Therefore, the thickness of the oceanic crust is not 15 km, and the thickness of the continental crust is not around 30 km.

In summary, the correct statement is option 1, while option 2 is incorrect.