Introduction:
GaAs is a compound semiconductor that has a diamond crystal structure. In order to fracture the crystal in the (001) plane, we need to understand the bonding arrangement in the crystal lattice and the nature of the bonds between Ga and As atoms.

Diamond Structure:
The diamond crystal structure consists of a repeating pattern of tetrahedrally bonded atoms. Each atom is covalently bonded to four neighboring atoms, forming a three-dimensional network. In GaAs, gallium (Ga) atoms occupy the tetrahedral voids of arsenic (As) atoms, and vice versa.

Bonding in GaAs:
GaAs is composed of covalent bonds between Ga and As atoms. The covalent bond is formed by the sharing of electrons between the atoms. In GaAs, each Ga atom shares three of its valence electrons with three neighboring As atoms, while each As atom shares one of its valence electrons with a neighboring Ga atom. This results in a strong, directional bond.

Fracture in the (001) Plane:
To fracture the GaAs crystal in the (001) plane, we need to break the Ga-As bonds along this plane. In the (001) plane, the atoms are arranged in a square lattice.

Bond Breaking:
To understand the number of Ga-As bonds that need to be broken, we can visualize the (001) plane of the GaAs crystal. In this plane, each Ga atom is bonded to four neighboring As atoms, and each As atom is bonded to four neighboring Ga atoms.

When we fracture the crystal in the (001) plane, we need to break the bonds between Ga and As atoms. In this plane, each Ga atom is bonded to two As atoms in the plane and two As atoms above and below the plane. Similarly, each As atom is bonded to two Ga atoms in the plane and two Ga atoms above and below the plane.

Conclusion:
Therefore, in order to fracture the GaAs crystal in the (001) plane, we need to break four Ga-As bonds per atom. This is because each Ga atom is bonded to four As atoms in total, and each As atom is bonded to four Ga atoms in total. Hence, the correct answer is '4'.