Final answer:
The correct hardware prerequisite for ESXi 6 is 10 GB of available disk space. Options regarding RAM, CPU, and a floppy disk drive are incorrect as they do not meet the minimum requirements for the installation of ESXi 6.
Step-by-step explanation:
The correct hardware prerequisite for VMware ESXi 6 installation is C) 10 GB of available disk space.
A minimum of 4 GB RAM is required (making option A incorrect), and ESXi 6 requires at least a 1.5 GHz Intel x86 or AMD processor (making option B incorrect). Option D, a floppy disk drive, is not a requirement for modern server installations such as ESXi 6, making this option also incorrect.