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Answer:
Beats are the difference in frequency.
(a) is correct option.
Explanation:
Beat :
Beat is the difference of the frequency of two waves.
The difference in frequency is equal to the number of beat per second.
Amplitude :
Amplitude of the wave is the maximum displacement.
Frequency :
Frequency is the number oscillations of wave in per second.
Intensity :
Intensity is the power per unit area.
Hence, Beats are the difference in frequency.
Answer:
42 m/s
Explanation:
by definition of the velocity(speed) of a wave,
The velocity of light, v, is the product of its wavelength, λ , and its frequency, f.
V= fλ
frequency - number of occurances in a unit time
(check the graph)

Before answering this question, you must know the concept between extensive and intensive property. The extensive property does not depend on the amount of substance (like mass), which is the opposite of intensive properties. From the given choices, the rest are extensive properties except for <em>amount of matter</em>. Hence, that is the answer.
There is no kinetic energy.
Kinetic energy = 1/2(m)v^2
There is no velocity; therefore, there is no kinetic energy.