Add useHook and its usage question

Author: sudheerj

README.md

@@ -6228,7 +6228,8 @@ Technically it is possible to write nested function components but it is not sug
      ```
 
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-275. ###  What types of values can `useState` hold?
+
+275. ### What types of values can `useState` hold?
 
      The `useState` hook accepts different types of values.
 
@@ -6245,6 +6246,7 @@ Technically it is possible to write nested function components but it is not sug
      setUser(prev => ({ ...prev, name: 'Sudheer' })); //correct way
      ```
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+
 276. ### What happens if you call `useState` conditionally?
      As per rules of React Hooks, hooks must be called unconditionally. For example, if you conditionally call it:
      ```js
@@ -6255,6 +6257,7 @@ Technically it is possible to write nested function components but it is not sug
 
      React will throw a runtime error because it **relies on the order of Hook calls**, and conditional logic breaks that order.
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+
 277. ### Is useState Synchronous or Asynchronous?
      The `useState` hook is synchronous, but state updates are asynchronous. When you call `useState()`, it runs synchronously and returns the state variable and setter function as tuple.
      ```js
@@ -6376,6 +6379,22 @@ Technically it is possible to write nested function components but it is not sug
       
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+279. ### What is `useReducer`? Why do you use useReducer?
+     The `useReducer` hook is a React hook used to manage **complex state logic** inside **functional components**. It is conceptually similar to **Redux**. i.e, Instead of directly updating state like with `useState`, you **dispatch an action** to a **reducer function**, and the reducer returns the new state.
+
+     The `useReducer`  hook is used when:
+
+     *   The **state is complex**, such as nested structures or multiple related values.
+     *   State updates depend on the **previous state** and **logic**.
+     *   You want to **separate state update logic** from UI code to make it cleaner and testable.
+     *   You’re managing features like:
+         *   Forms
+         *   Wizards / Multi-step flows
+         *   Undo/Redo functionality
+         *   Shopping cart logic
+         *   Toggle & conditional UI logic
+     **[⬆ Back to Top](#table-of-contents)**
+
 ## Old Q&A
 
 1. ### Why should we not update the state directly?