When two icecubes are pressed together, they join to form one cube. Which one of the following helps to hold them together?

When two ice cubes are pressed together, they join to form a single block primarily due to the formation of hydrogen bonds. Water molecules in ice are polar, with oxygen carrying a partial negative charge and hydrogen carrying a partial positive charge [t2]. In the solid state, these molecules are held in a tetrahedral lattice by hydrogen bonds [t5]. Pressing the cubes together can cause a thin layer of surface melting (regelation) or simply bring the surface molecules into close enough proximity for the positively charged hydrogen atoms of one cube to attract the negatively charged oxygen atoms of the other [t1, t2]. This electrostatic attraction establishes new hydrogen bonds across the interface, effectively merging the two separate structures into one continuous crystalline lattice [t2, t3]. While Van der Waals forces and dipole interactions exist, the specific strength and directional nature of hydrogen bonding are the dominant factors in ice formation and cohesion [t2, t5].

Sources

1. [1] https://en.wikipedia.org/wiki/Phases_of_ice