Question

Which of the following numbers is not a perfect cube?

• A. 343
• B. 1331
• C. 729
• D. 625

Answer 1

The correct option is D 625

$343=7\times 7\times 7$​
$1331=11\times 11\times 11$ ​
$729=9\times 9\times 9$
$625=5\times 5\times 5\times 5$
For a number to be a perfect cube, each of its factors must be repeated thrice. 343, 1331 and 729 are the perfect cubes of 7, 11 and 9 respectively, whereas 625 is not, as 5 is repeating 4 times which is not a triplet. ​
625 is not a perfect cube.