As we know that Nth harmonic of the string is given by
[tex]f = \frac{N}{2L}\sqrt{\frac{T}{m/L}}[/tex]
now here we will have
[tex]m/L = mass density = 2 g/m[/tex]
[tex]m/L = 0.002 kg/m[/tex]
[tex]Length = L = 0.600 m[/tex]
[tex]Tension = T = 50.0 N[/tex]
now from above formula we have
[tex]f = \frac{N}{2(0.600)}\sqrt{\frac{50.0}{0.002}}[/tex]
[tex]f = 131.8N [/tex]
now for first harmonic N = 1
[tex]f_1 = 131.8 Hz[/tex]
for second harmonic N = 2
[tex]f_2 = 263.5 Hz[/tex]
for third harmonic N = 3
[tex]f_3 = 395.3 Hz[/tex]