An audio frequency of 5 kHz is translated to a radio frequency carrier of frequency 1 MHz and transmitted it to space through an antenna. The required height of antenna is

ANS:A - 150 m

For the transmission of Radio signals, the antenna height must be multiple of λ/4 .Where;
λ is the wavelength λ=c/f where c is speed of light and f is the frequency of the signal to be transmitted.
So,
λ/4 =c/4f = 3*10^3/ 4*1*10^6 = 75 meter.
So the answer should be (C).

Note:- Do not take carrier signal instead of message signal @Sateesh.