Final answer:
The circle on the integral symbol when integrating b(r) indicates a closed path and signifies a line integral, which is Option 3: Line integral.
Step-by-step explanation:
In mathematical notation, the circle on the integral symbol signifies a specific type of integral. Specifically, when you see a circle through the integral sign while integrating a function like b(r), it denotes a closed path or closed surface.
For the options provided, the correct answer is: Option 3: Line integral. This is because when integrating over a closed loop or path, the circle indicates you are performing a line integral over a closed curve.
A surface integral would typically be indicated by a double integral sign without the circle through it, and is used when you want to calculate the flux through a surface, for example.
Triple integrals are used for computing volumes in three dimensions and would not typically have the circle notation. As for the discussion about the volume and surface area of a sphere, the formula 4πr^3/3 represents the volume, whereas 4πr^2 is the surface area.