What is the purpose of using access modifier <b>mu

What is the purpose of using access modifier mutable?

For the same purpose as a const keyword in C
To allow modification of the class member which belongs to a constant object
There is no such modifier in C ++
To allow modification of a static member of the class
For the same purposes as the volatile modifier

C ++ Standard - ANSI ISO IEC 14882 2003 § 7.1.1.9 The mutable specifier on a class data member nullifies a const specifier applied to the containing class object and permits modification of the mutable class member even though the rest of the object is const