Answer
(a) String 1 has a greater tension. (b) Choice I.
Work Step by Step
The speed of a wave on a string is equal to $$v=\sqrt{\frac{F_T}{\mu}}$$ Solving for $F_T$ yields $$F_T=\mu v^2$$ Therefore, if velocity remains the same and the linear mass density $\mu$ increases, the tension must increase. Therefore, as the string becomes thicker and has a larger mass density, the tension must be greater. This means that the thicker string, string 1, will have greater tension.
