Chose the correct term to complete the sentence.

The Constant or identity function is a linear function described by $f\left(x\right)=x$

A constant function is used to represent a quantity that stays constant over the course of time and it is considered to be the simplest of all types of real-valued functions. Constant functions are linear functions whose graphs are horizontal lines in the plane. The maximum marks which can be obtained in an examination can be taken as one of the real-life examples of constant functions.

The identity function is a linear polynomial function. It is defined as$g:R\to R$such that$g\left(x\right)=x$ The domain is equal to the range for an identity function.

From two function its clear that the sentence which make sense is the Identity function

Since, the definition state that

The identity function is a linear polynomial function. It is defined as$g:R\to R$such that$g\left(x\right)=x$ The domain is equal to the range for an identity function.

Therefore, the correct statement to complete the sentence isIdentity.