Here are 20 fundamental questions for beginners in ReactJS:

React Basics:

1. What is ReactJS, and how does it differ from other JavaScript frameworks?

2. Explain the concept of a virtual DOM in React.

3. How do you create a new React application using Create React App?

Components and JSX:

1. What is a React component, and how do you create one?

2. Explain the purpose of JSX in React.

3. How do you render a component in React?

Props and State:

1. What are props in React, and how are they used to pass data between components?

2. Describe the difference between states and props in a React component.

3. How do you update the state of a component in React?

Component Lifecycle:

1. List and explain the main phases of the React component lifecycle.

2. How can you perform side effects in a React component using lifecycle methods?

Handling Events:

1. How do you handle events in React?

2. Explain the importance of binding for event handlers.

Conditional Rendering:

1. How can you conditionally render components in React?

2. What is the purpose of the ternary operator in conditional rendering?

Lists and Keys:

1. How do you render a list of elements in React?

2. Explain the significance of keys when rendering lists in React.

Forms in React:

1. How do you handle form inputs and form submissions in React?

2. What is controlled and uncontrolled components in React forms?

React Router:

1. What is React Router, and how do you implement client-side routing in a React application?

Conclusion:

These questions cover the basics of ReactJS, including components, props, state, lifecycle, events, conditional rendering, lists, keys, forms, and React Router. They serve as a foundation for understanding React and building more complex applications.