Continuous spectrum is not produced by which of the following?

The colour of the positive column in a gas discharge tube depends on

Which of the following elements was discovered by the study of Fraunhofer lines?

The splitting of a spectral line into groups under the effect of an electric or magnetic field is called:

$A$ neutron collides head-on with a stationary hydrogen atom in its ground state.

In a Franck-Hertz experiment,an electron of energy $5.6 \ eV$ passes through mercury vapour and emerges with an energy $0.7 \ eV$. The minimum wavelength of photons emitted by mercury atoms is close to ............. $nm$.