The number of the following statements which is/are incorrect is:
$A$. Line emission spectra are used to study the electronic structure.
$B$. The emission spectra of atoms in the gas phase show a continuous spread of wavelength from red to violet.
$C$. An absorption spectrum is like the photographic negative of an emission spectrum.
$D$. The element helium was discovered in the sun by spectroscopic method.

• A
  $2$
• B
  $1$
• C
  $3$
• D
  $0$