(A) (1, 5, 10)

Here 1^{2}+5^{2} ≠ 10^{2}

The square of largest number is not equal to sum of squares of the other two numbers.

So (1, 5, 10) is not a Pythagorean triplet.

(B) (3, 4, 5)

Here 3^{2}+4^{2 }= 5^{2}

The square of largest number is equal to sum of squares of the other two numbers.

So (3, 4, 5) is a Pythagorean triplet.

(C) (2, 2, 2)

Here 2^{2}+2^{2} ≠ 2^{2}

The square of largest number is not equal to sum of squares of the other two numbers.

So (2, 2, 2) is not a Pythagorean triplet.

(D) (5, 5, 2)

Here 2^{2}+5^{2} ≠ 5^{2}

The square of largest number is not equal to sum of squares of the other two numbers.

So (5, 5, 2) is not a Pythagorean triplet.

Hence option B is the correct answer.