Answer:
Pendulum B
Step-by-step explanation:
The time period of a pendulum is given by :

Case 1.
Mass, m = 200 g = 0.2 kg
Length of string, l = 1 m
Time,

T₁ = 2.007 Seconds
Since,


f₁ = 0.49 Hz
Case 2.
Mass, m = 400 g = 0.4 kg
Length of string, l = 0.5 m
Time,

T₂ = 1.41 seconds


f₂ = 0.709 seconds
Hence, pendulum B have highest frequency of vibration.