The question asks us to identify the type of function whose range consists of only one element. The options are: onto function, one-to-one function, constant function, and identity function.

1. Problem Description

The question asks us to identify the type of function whose range consists of only one element. The options are: onto function, one-to-one function, constant function, and identity function.

2. Solution Steps

Let's examine each option:

* Onto function: A function $f: A \rightarrow B$ is onto (or surjective) if for every element $b$ in $B$, there is at least one element $a$ in $A$ such that $f(a) = b$. This means the range of $f$ is equal to its codomain. The range can have more than one element.

* One-to-one function: A function $f$ is one-to-one (or injective) if $f(x_1) = f(x_2)$ implies $x_1 = x_2$. This means each element in the range corresponds to a unique element in the domain. The range can have more than one element.

* Constant function: A constant function is a function whose output is the same value for every input. For example, $f(x) = c$ for some constant $c$. In this case, the range contains only the element $c$.

* Identity function: An identity function is a function that returns the same value that was used as its argument. For example, $f(x) = x$. The range will have multiple elements.

Therefore, a function whose range consists of only one element is a constant function.

3. Final Answer

(3) Constant function.