Which of the following dimensions represents a cubic unit cell?

$a=b=c;\alpha =\beta =\gamma ={90}^{\circ }$ of the following dimensions represents a cubic unit cell.

In a simple cubic structure, the simple cubic unit cell is the most basic repeating unit. A lattice point where an atom, ion, or molecule may be found in the crystal defines each corner of the unit cell. By convention, a unit cell's edge always links equal points.

Hence option A is correct.