Which of these is an invalid identifier?

Can an identifier be a single character?

A). Yes

B). No

C). Only in ES5

D). Only in ES6

Can JavaScript identifiers include spaces?

A). Yes

B). No

C). Only in ES6

D). Only in strings

What is the output of the following code: var x = 5, x = 10;

A). Syntax error

B). 5

C). 10

D). Reference error

What will happen if you declare a variable with the name undefined?

A). Syntax error

B). Declares a variable

C). Throws a runtime error

D). Reassigns undefined

Which of the following is a reserved word in JavaScript?

A). myVariable

B). function

C). let

D). number

Are JavaScript identifiers case-sensitive?

A). Yes

B). No

C). Only in ES6

D). Only in strict mode

Can identifiers start with a digit in JavaScript?

A). Yes

B). No

C). Only in ES5

D). Only in strict mode

What will be the result of using a reserved word as an identifier?

A). No error

B). Syntax error

C). Logical error

D). Runtime error

Which of the following is an invalid identifier?

A). _variable

B). var$

C). 2variable

D). variable2

What is a valid identifier in JavaScript?

A). 123abc

B). abc123

C). let

D). var