The repeating subunits that are responsible for the shape of a crystal are known as
unit cells.
heavy nuclei.
light electrons.
amorphous cells.

The correct answer is unit cell.

Explanation:

Unit cell

Smallest unit of a crystal with fixed arrangement of atoms or ions. And this geometrical arrangement of atoms is responsible for shape of crystal and symmetry possessed by the crystal. Repetition of these unit cells in a space forms crystal.

14,16 18 reacts with group

c (diamond),

sio2 (quartz)