Answer: Option 'B' is correct.
Explanation:
We need to find the side lengths that form a right triangle ,
To find the pythagorean triplet ,we will use "Pythagorus theorem", which states that

As we have given that
A) 7 cm, 8 cm, 10 cm
We'll check for this

so, it can't be the side of right triangle.
B) 15 m, 20 m, 25 m
We'll check for this

Hence, it is correct set of side lengths that form a right triangle.
On the other hand, C) and D) are not satisfying the pythagorus theorem,
because,

Hence, Option 'B' is correct.