An identity is an equation that is true for all real numbers.
Explanation:
An identity is a mathematical statement that is always true. It does not matter what numbers you substitute in for the variables, the result will be the same.
I think the correct answer from the choices listed above is the second option. The most accurate definition of an identity is that an identity is an equation that is true for all real values in its domain. It is also an equality relation that no matter what values are chosen the equation is still true.
