Which keyword is used for declaring variables that should not change?

What will be the output of the following code: const d = 90; d = 100; console.log(d);

A). 90

B). 100

C). Error

D). undefined

What will be the output of the following code: console.log(a); var a = 50;

A). 50

B). undefined

C). Error

D). null

What is the default scope of variables declared with the 'var' keyword in JavaScript?

A). Block scope

B). Function scope

C). Module scope

D). Block and function scope

How does 'let' differ from 'var' in terms of scope?

A). No difference

B). Function-scoped

C). Block-scoped

D). Global-scoped

Which keyword allows block-scoped variable declaration?

A). var

B). let

C). const

D). Both B and C

How does 'let' handle variable re-declaration in the same scope?

A). Allows it

B). Silently ignores

C). Throws an error

D). Creates a new variable

What is the scope of a variable declared with 'let' inside a loop?

A). Global

B). Function

C). Loop block

D). Entire script

Can you re-declare a variable using 'const' in the same scope?

A). Yes

B). No

C). Only in functions

D). Only in loops

What will be the output of the following code: let y = 10; let y = 20; console.log(y);

A). 10

B). 20

C). Error

D). undefined

Can 'const' be used to declare an array or object?

A). No, only primitives

B). Yes, but the reference can't change

C). Yes, and the content can't change

D). No