Question

Which of these is not a perfect cube?

• A. 343
• B. 1331
• C. 512
• D. 81

Answer 1

The correct option is D

81

By prime factorization, we have

$343=7\times 7\times 71331=11\times 11\times 11512=8\times 8\times 881=3\times 3\times 3\times 3$

For a number to be a perfect cube ,each of its factors must be repeated thrice.
343, 1331 and 512 are the perfect cubes of 7, 11 and 8 respectively, whereas 81 is not, as 3 is repeating 4 times which is not a triplet.

81 is not a perfect cube.