List the ordered pairs from the table, then check that each roll number has exactly one mark — repeated marks for different students are not a problem.

Ordered pairs. Reading the table row by row:

Checking the function conditions. Every roll number $1$ through $5$ appears exactly once as a first co-ordinate, and each is paired with exactly one mark. It does not matter that the mark $45$ is repeated (for roll numbers 1 and 3) or that $60$ is repeated (for roll numbers 2 and 5) — the function condition only requires that each input (roll number) has a single output; it places no restriction on outputs repeating. So this relation is a function.

Domain = set of roll numbers actually used = $\{1, 2, 3, 4, 5\}$.

Range = set of distinct marks actually obtained = $\{45, 60, 78\}$ (listed once each, even though $45$ and $60$ each occur twice).

Independent cross-check: counting the table directly — 5 roll numbers, 5 ordered pairs, no roll number missing and none repeated as a first element — confirms the function condition holds exactly as concluded.

Wrongly concluding it is NOT a function because two students share the same mark — a function only forbids one roll number from having two different marks, not two roll numbers sharing one mark. Also, listing the range with repeated values (45, 60, 45, 78, 60) instead of as a set of distinct values.