​A = {24, 36, 48} and B = {12, 18, 24), f : A → B. Which of the following functions is neither one-one nor onto where f : N → N?​

Correct option is D

​$$\begin{aligned}&\textbf{Option 1:} \quad f = \{(24,\ 12),\ (36,\ 18),\ (48,\ 24)\} \\[4pt]&\bullet\ \text{All elements in } A \text{ map to distinct elements in } B: \ {\text{one-one}} \\&\bullet\ \text{All elements in } B \text{ are covered:} \ {\text{onto}} \\&{\text{This function is both one-one and onto}} \\[12pt]&\textbf{Option 2:} \quad s = \{(24,\ 24),\ (36,\ 12),\ (48,\ 18)\} \\[4pt]&\bullet\ \text{All inputs have unique outputs:} \ {\text{one-one}} \\&\bullet\ \text{All elements in } B \text{ appear:} \ {\text{onto}} \\&{\text{Also one-one and onto}} \\[12pt]&\textbf{Option 3:} \quad g = \{(24,\ 18),\ (36,\ 24),\ (48,\ 12)\} \\[4pt]&\bullet\ \text{No repeated outputs:} \ {\text{one-one}} \\&\bullet\ \text{All values from } B \text{ are used:} \ {\text{ onto}} \\&{\text{Again one-one and onto}} \\[12pt]&\textbf{Option 4:} \quad h = \{(24,\ 12),\ (36,\ 18),\ (48,\ 12)\} \\[4pt]&\bullet\ \text{Both 24 and 48 map to 12:} \ {\text{Not one-one}} \\&\bullet\ \text{24 from set } B \text{ is not mapped to:} \ {\text{Not onto}} \\&{\text{This function is neither one-one nor onto}}\end{aligned}$$​​