Crystal System
The crystal system is characterized by the shape and symmetry of the unit cell in a crystal lattice. In this case, A atoms are arranged in a ccp (cubic close-packed) arrangement.

B Atom Arrangement
B atoms occupy all octahedral voids and half of the tetrahedral voids in the ccp arrangement of A atoms. This means that for every two A atoms, there is one B atom occupying a tetrahedral void and one B atom occupying an octahedral void.

Formula Representation
The formula representation of this crystal system can be determined by calculating the ratio of A atoms to B atoms. Since there are two types of voids that B atoms occupy, we need to consider both types in our calculation.

For every two A atoms, there is one B atom occupying a tetrahedral void. Therefore, the ratio of A atoms to tetrahedral voids is 2:1. Similarly, for every four A atoms, there are two B atoms occupying octahedral voids. Therefore, the ratio of A atoms to octahedral voids is 4:2, which simplifies to 2:1.

Combining these ratios, we get the formula representation of AB2, where A represents the atoms in the ccp arrangement and B represents the atoms occupying the voids.

Summary
In summary, the crystal system consists of A atoms arranged in a ccp arrangement with B atoms occupying all octahedral voids and half of the tetrahedral voids. The formula representation of this system is AB2, where A represents the atoms in the ccp arrangement and B represents the atoms occupying the voids.

 FCC