Final answer:
In AWS, a spread placement group can contain up to 7 running instances per Availability Zone, and it helps to minimize correlated failures without occupying a whole rack.
Step-by-step explanation:
The number of instances that can be within a spread placement group in cloud computing environments, such as Amazon Web Services (AWS), typically depends on the specific platform and the type of instance. In AWS, a spread placement group is a grouping of instances that are each placed on distinct underlying hardware to reduce the risk of simultaneous failures. It is designed for applications that need to minimize correlated failures but do not use enough instances to require using an entire rack. AWS documentation states that each spread placement group can have up to 7 running instances per Availability Zone.