The number of following statement/s 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

Analyzing each statement about atomic spectra:

A) Line emission spectra are used to study the electronic structure.

This is correct. Line spectra reveal the energy levels and electronic structure of atoms.

B) The emission spectra of atoms in the gas phase show a continuous spread of wavelength from red to violet.

This is incorrect. Atoms in the gas phase produce line spectra (discrete wavelengths), not continuous spectra. Continuous spectra are produced by hot solids or dense gases.

C) An absorption spectrum is like the photographic negative of an emission spectrum.

This is correct. Where emission spectra show bright lines against a dark background, absorption spectra show dark lines at the same wavelengths against a bright background.

D) The element helium was discovered in the sun by spectroscopic method.

This is correct. Helium was first identified in the solar spectrum by Lockyer and Janssen in 1868, before being found on Earth.

Only statement B is incorrect.

The number of incorrect statements is 1.