The number of incorrect statement/s about the black body from the following is __________
(A) Emit or absorb energy in the form of electromagnetic radiation.
(B) Frequency distribution of the emitted radiation depends on temperature.
(C) At a given temperature, intensity vs frequency curve passes through a maximum value.
(D) The maximum of the intensity vs frequency curve is at a higher frequency at higher temperature compared to that at lower temperature.

Solution

Chemistry ma’am · 4 steps

Picture the black-body curves at two temperatures: every statement here describes them correctly.

1. Absorb and emit. An ideal black body absorbs all radiation falling on it and is also the best possible emitter. Both processes happen as electromagnetic radiation, so (A) is correct.
2. Depends on temperature. How the emitted energy is spread over frequencies depends only on the temperature of the black body, not on what it is made of. So (B) is correct.

   Feature of the curve	What happens	Statement
   Shape at one temperature	Intensity rises with frequency, reaches a peak, then falls	(C) correct
   Peak as T increases	Peak moves to higher frequency (shorter wavelength)	(D) correct

3. Why the peak shifts. Wien's law gives λₘₐₓ T = constant, so a hotter body has a smaller λₘₐₓ and a larger νₘₐₓ. This is why heated iron glows red first and then turns white-hot.
4. So. All four statements are correct, so the number of incorrect statements is 0.

The common slip: 1. Thinking the peak moves to lower frequency as the body heats up marks (D) as wrong and gives 1. Wien's law moves the peak to shorter wavelength, which means higher frequency.

The idea to keep. Black-body radiation depends only on temperature. Each curve has one peak, and a hotter body peaks at a higher frequency, which is Wien's law.

Answer from the NTA final answer key. Solution by PrepWiser.