We are given the following radical expression:
[tex]\sqrt[]{a+b}[/tex]We are asked to determine the equivalent exponential expression. To do that we will use the following relationship:
[tex]\sqrt[]{x}=x^{\frac{1}{2}}[/tex]Applying the relationship we get:
[tex]\sqrt[]{a+b}=(a+b)^{\frac{1}{2}}[/tex]Therefore, the right answer would be B.