Public cloud grants accessibility of systems and various services to general public. Eg: Google, Microsoft, Amazon etc. Advantages and Disadvantages of Public Cloud is as follows;

Advantages

1. Cost Effective - Public cloud share same resources with large number of consumer. So it is avialable for low cost.
2. Reliability - Public cloud implements large number of resources from different locations. Therefore when any resource fail, public cloud is able to implement another resource allowing uninterrupted service.
3. Flexibility - Public cloud can be easily integrate with private cloud, giving consumers a flexible approach.
4. Location Independent - Public Cloud is delivered through internet, which means anyone can access public cloud regardless the location.
5. Utility Style Costing - Public cloud is based on pay-per-use model
6. High Scalability - Public Cloud  can be scaled up or down according the requirement.

Disadvantages 

1. Low Security - Major disadvantage of Public cloud is security. Since data that is hosted in public cloud is off-site and resources are shared publicly, there is a security and privacy issue.
2. Less Customizable - It is comparatively less customizable than private cloud.