Which form factor measures 9.6" squared and allows only four expansion cards?

The Micro-ATX form factor is indeed characterized by its dimensions of 9.6 inches squared and is designed to accommodate up to four expansion cards. This makes it a versatile option suitable for compact builds while still offering sufficient space for essential expansion and connectivity. The Micro-ATX provides a balance between size and functionality, enabling users to connect various components such as graphics cards, sound cards, or additional storage controllers without needing a full-sized motherboard.

The other options represent different sizes and capabilities. Standard ATX, for example, is larger and allows for more expansion options, while Mini-ITX is even more compact and usually supports fewer upgrades, typically just one expansion card. Mini-ATX is not a widely recognized standard in the industry, which could lead to some confusion about its specifications. Thus, Micro-ATX is the most accurate answer in the context of the question regarding the specified measurements and the limit on expansion cards.