In amplitude modulation, the A.F (Audio-frequency) modulating wave is superimposed on a R.F (radio-frequency)carrier wave in such a manner that :
A) The frequency of the modulated wave is the same as that of the carrier wave.
B) The amplitude of the modulated wave is the same as that of the carrier wave.
C) It’s amplitude varies in accordance with instantaneous amplitude of the modulating wave.
D) The frequency of the carrier wave is changed in accordance with the amplitude of the modulated wave.

Hint:Amplitude modulation – it is a modulation method used in communication. In amplitude modulation , the amplitude of the carrier wave is varied in proportion to that of A.F ( audio – frequency) signals.

Complete step by step solution:
 Amplitude modulation means modulation of amplitude of the signal (Audio – frequency ).
In amplitude modulation the A.F (Audio-frequency) modulating wave is superimposed on a R.F (radio-frequency)carrier wave in such a manner that It’s amplitude varies in accordance with instantaneous amplitude of the modulating wave.

Hence option ( C ) is correct.

Note :- Modulation- The phenomenon of superposition of information signal over a high frequency carrier wave is called modulation .

Need for Modulation
-To avoid interference
-To design the antennas of practical size
-To determine the effective power radiated by an antenna.

Signal - signal is the information converted in electrical form. Signals can be analog or digital.
-Analog signal - A continuously varying signal ( Voltage OR Current ) is called an analog signal. A decimal number with system base 10 is used to deal with analog signals.
Few examples that we see like TV signals and picture signals are Analog in nature.
Also human voice or in fact any kind of natural voice is of kind of analog signal.
-Digital signal - A digital signal is that type of signal that means the kind of signal that only discrete stepwise values is called a digital signal. A binary system with base 2 is used for dealing digital signals.
Few examples of digital signals optical drives and computers.