Answer:
Option B is irrational.
Explanation:
The question on the picture says "Which of the following is an irrational number?".
√84 is irrational because it is not a perfect square.
So, option B is the correct answer to the question pictured.
If you still need them:
A and D are perfect squares so they are rational.
√49 = 7
√16 = 4
1.7 is a real number, so it is rational.