The answer is the first option. The one about doing your best. trust me I read the book today!
here since string is attached with a mass of 2 kg
so here tension force in the rope is given as

here we will have

now we will have speed of wave given as

here we will have


now we know that frequency is given as
F = 100 Hz
now wavelength is given as


so wavelength will be 0.16 m
If n=1 you divide by 2
If n=2 you divide by 4
If n=3 you divide by 8
so any n you divide by 2 to the power n