JEE Chemistry 2023 Question with Solution

Given: Four statements about emission and absorption spectra are listed.

Find: The number of incorrect statements and hence the correct option.

Check each statement:

1. Statement A is correct. Line emission spectra are used to study electronic structure.
2. Statement B is incorrect. Atomic emission spectra in the gas phase are discontinuous and consist of distinct lines, not a continuous spread from red to violet.
3. Statement C is correct. An absorption spectrum is like the photographic negative of an emission spectrum.
4. Statement D is correct. Helium was first discovered in the sun by spectroscopy.

Therefore, only one statement is incorrect. The correct option is B.

The key idea is that isolated atoms in the gaseous state show line spectra because electrons can move only between discrete energy levels.

• A: True.
• B: False because a continuous spectrum is not shown by isolated gaseous atoms; they show line emission spectra.
• C: True because dark lines in absorption occur at the same wavelengths as bright lines in emission.
• D: True because helium was identified in the solar spectrum before it was isolated on Earth.

Hence the number of incorrect statements is $1$, so the correct option is B.