Answer-1. 'var' is function-scoped, can be redeclared, and is hoisted with undefined. 'let' is block-scoped, cannot be redeclared, and is hoisted but not initialized. 'const' is block-scoped, cannot be redeclared or reassigned, and is hoisted but not initialized.

Answer-2. 'map()' transforms elements and returns a new array. 'forEach()' runs a function on each element but does not return a new array. 'filter()' returns a new array with elements that pass a condition.

Answer-3. Arrow functions (=>) are a shorter syntax for writing functions in JavaScript. A. 'this' binding: Arrow functions do not have their own 'this'; they inherit it from the surrounding scope. B. Syntax: Arrow functions are more concise and do not require the function keyword. C. Cannot be used as constructors: Unlike regular functions, arrow functions cannot be used with 'new'. D. No arguments object: Arrow functions do not have their own arguments object.

Answer-4. A Promise is an object that represents the eventual completion (or failure) of an asynchronous operation. There are 3 possible states of a Promise such as a. Pending: The initial state, operation not yet completed. b. Fulfilled: The operation was successful. c. Rejected: The operation failed. To handle a Promise we can use '.then()' for success, '.catch()' for errors, and '.finally()' for code that runs regardless of success or failure. 'async/await' makes working with Promises easier by allowing asynchronous code to look like synchronous code.

Answer-5. A Closure is a function that remembers and can access variables from its outer scope even after the outer function has finished executing. A function "closes over" the variables it depends on, keeping them in memory even after the outer function returns. It is useful in creating private variables, managing states in functional programming, event handling and callbacks.