Answer:
Option D
Explanation:

T cosθ component will cancel mg
Tsinθ component will provide necessary centripetal force to the ball towards centre C
∴ Tsinθ=mrω2=m(lsinθ)ω2
∴ ω=√Tml
or ωmax=√Tmaxml=√3240.5×0.5
=36 rad/s
∴ correct option is (d)
Analysis of Question
(i) Question is simple
(ii) This is called the conical pendulum
(iii)The interesting fact in this problem is that ω or T is independent of θ
ω∝√T
If ω is increased, T will also increase