The best example of a smart assistant from the options provided is Google Nest. Google Nest encompasses a range of smart home devices, including smart speakers and displays that utilize Google Assistant, which is a virtual assistant that can perform tasks, answer questions, and control smart home devices using voice commands.
The other options listed, such as Google Classroom, Google Chrome, and Google Cloud Platform, are tools and services focused on education, web browsing, and cloud computing, respectively, rather than functioning as smart assistants.