The light emitted by an incandescent element produces: ~a unique continuous spectrum ~an emission line spectrum ~a spectrum identical to the hydrogen atom ~a spectrum of one unique wavelength

 an emission line spectrum

Explanation:  An emission line spectrum is produced form the light emitted by the incandescent lamp.

Line Spectrum is produced when the electron that has been excited to the higher energy state levels moves between the molecular energy levels while returning to the ground state.

Incandescent lamp is the lam that generates electricity when electrical current runs through it.

nacl is added to the aqueous of what? ? in order to get a proper answer you have to specify the exact composition of the aqueous solution.