Answer:
Option B,C
Explanation:

Number of nodes =6
From the given equation , we can see that
k=2πλ=62.8m−1
∴ λ=2π62.8m=0.1m
l=5λ2m=0.25m
The mid point of the string is P ,an antinode
∴ maximum displacement=0.01 m
ω=2πf=628s−1
∴ f=6282π=100Hz
But this si fifth harmonic freequency .
∴ Fundamental frequency f0
=f5=20Hz