What is backend.
What is difference between mongodb and SQL.
React router methods.
How you will implement the login function.
What is database.
What is mongodb.
What is ApI and different rest methods we use?

1. **What is backend?**
   - The backend refers to the server-side of web development where data processing, logic, and database interactions occur.

2. **Difference between MongoDB and SQL?**
   - MongoDB is a NoSQL database that stores data in JSON-like documents, while SQL databases (such as MySQL, PostgreSQL) store data in structured tables with rows and columns. MongoDB is schema-less, allowing flexible data models, whereas SQL databases have a fixed schema.

3. **React Router methods?**
   - React Router provides methods like `BrowserRouter` for web applications, `HashRouter` for hash-based routing, `Route` for defining routes, `Link` for navigation, and `Switch` for rendering the first matching route.

4. **How will you implement the login function?**
   - Implementing a login function involves creating a login form with input fields for username and password, handling form submission, sending a POST request to the server with user credentials, verifying credentials on the server, and setting up authentication mechanisms like JWT or sessions.

5. **What is a database?**
   - A database is an organized collection of structured data stored electronically in a computer system. It allows data to be easily accessed, manipulated, and managed.

6. **What is MongoDB?**
   - MongoDB is a NoSQL database management system that uses a document-oriented database model. It stores data in flexible, JSON-like documents with dynamic schemas, making it easy to manage and scale.

7. **What is API and different REST methods we use?**
   - An API (Application Programming Interface) is a set of rules and protocols that allows different software applications to communicate with each other. REST (Representational State Transfer) is an architectural style for designing networked applications. Common REST methods include GET (retrieve data), POST (create data), PUT (update data), DELETE (remove data), and PATCH (partially update data).