What will be the output of the following code?

console.log(a); var a = 10;

Which of the following is true about variable naming conventions in JavaScript?

A). Variable names can start with a number

B). Variable names are case-insensitive

C). Variable names can include spaces

D). Variable names are case-sensitive

Which of the following is correct about variable scope in JavaScript?

A). var is block-scoped

B). let is function-scoped

C). const is block-scoped

D). All variables are global

Which keyword is used to declare a variable in JavaScript?

A). var

B). let

C). const

D). All of the above

Which of the following will cause an error?

A). let a = 10; a = 20;

B). const a = 10; a = 20;

C). var a = 10; a = 20;

D). None of the above

Which of the following is true about 'const' variables in JavaScript?

A). They can be redeclared

B). They cannot be reassigned

C). They can be reassigned

D). They are always undefined

Which of the following is a valid variable name in JavaScript?

A). 2name

B). _name

C). #name

D).

Which statement is true about variables in JavaScript?

A). They must be declared before use

B). They can only hold numbers

C). They are statically typed

D). They are strongly typed

What is hoisting in JavaScript?

A). Function call before declaration

B). Variable declared at the top

C). Variable and function declaration are moved to the top

D). Variable scope

Can you reassign a value to a variable declared with let?

A). Yes

B). No

C). Only in strict mode

D). Only inside a block

What will be the output of the following code?

let x; console.log(x);

A). null

B). undefined

C). 0

D). NaN