Q. A mapping $f:N \rightarrow N$, where $N$ is the set of natural numbers is defined as $f(n) = \left\{ \begin{array}{r} n^{2},\ for\ n\ odd \\ 2n + 1,\ for\ n\ even \end{array} \right.\$ For $n \in N$. Then, $f$ is

A) Surjective but not injective
B) Injective but not surjective
C) Bijective
D) Neither injective nor surjective
Explanation

(d)
Since, $f(n) = \left\{ \begin{array}{r}
n^{2},\ \ \ \ \ \ \ \ if\ n\ odd \\
2n + 1,\ \ \ if\ n\ is\ even
\end{array} \right.\$
$f(1) = 1^{2} = 1\ \ \ \ \ \ \ \ f(2) = 2(2) + 1 = 5$
$f(3) = 3^{2} = 9\ \ \ \ \ \ \ \ f(4) = 2(4) + 1 = 9$
$\therefore\ \ \ \ f(3) = f(4)$
$\therefore f$ is not injective.
Also, $f$ is not surjective as every element of $N$ is not the image of any element of $N$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.