Which of the following is an amorphous solid?

The major product in the following reaction is:

Arbor vitae is composed of

Haemocoel is found in

Cataract and skin cancer are caused by

Two soap bubbles of radii $r_1 = 4 \, cm$ and $r_2 = 5 \, cm$ are touching each other over a common surface $S_1S_2$ (as shown in the figure). The radius of curvature of this common surface will be ....... $cm$.