Which of the following could be a perfect square?
1681
Perfect squares cannot have 2, 3, 7 or 8 in their unit's place.
In the given options only 1681 does not end with a number other than these.
The perfect squares of numbers ending in 1 and 9 have 1 at their unit's place.
Thus, 1681 could be a perfect square of an integer ending with either 1 or 9.