Answer 1

What is the Difference?
Angular js and React js are intended to be Front end development frameworks. They concentrate more on how the data should be Shown to the user and To be Fast and Productive at the same time. Angular js Has a striking feature of two way binding of data, where when the source data changes, destination data changes too. So in a way they both are bound.
node js lets you execute the database queries by using javascript itself. So you dont need php.

Why Should we use them!
Angular js has a lot of features like two way data binding and $http post which is done flawlessly, also a lot of dependencies to use with which makes easier for the user to add and remove what u want and what you dont. It is also well structured so that You can understand the flow of data more efficiently.
Node js at the same time is a backend framework which contains different nodes for a particular requrest. And they are assigned to a port number. And each request is Given a port number and the server will execute the request.

Conclusion: All three frameworks are efficient. They have their pros and cons as well. It depends on the programmer how well they make use of it. Cheers, Happy coding.