Solution:

Excitation of Hydrogen Atom:

When a hydrogen atom is excited by a monochromatic radiation of wavelength λ, the electron jumps from its ground state to higher energy levels. When the electron returns to its ground state, it emits radiation of different wavelengths, producing a line spectrum.

Calculation of Wavelengths:

The excited state of the hydrogen atom can be calculated by the formula:

En = -13.6/n^2 eV

where n is the principal quantum number, and En is the energy of the nth level.

The energy difference between two levels can be calculated by the formula:

ΔE = Efinal - Einitial = hf

where ΔE is the energy difference, h is Planck's constant, and f is the frequency of the emitted radiation.

The frequency of the emitted radiation can be calculated by the formula:

f = c/λ

where c is the speed of light, and λ is the wavelength of the emitted radiation.

Using these formulas, we can calculate the wavelengths of the spectral lines emitted by the hydrogen atom.

Number of Spectral Lines:

The number of spectral lines emitted by the hydrogen atom depends on the number of energy levels that the electron jumps to and the number of energy level transitions that occur when the electron returns to its ground state.

For hydrogen, the possible energy level transitions are given by the formula:

ΔE = 13.6 (1/nf^2 - 1/ni^2) eV

where nf and ni are the final and initial quantum numbers, respectively.

The number of spectral lines emitted can be calculated by counting the number of possible energy level transitions that occur when the electron returns to its ground state.

For the given wavelength of 950 Å, the energy level transitions that occur when the electron returns to its ground state are:

- from n=2 to n=1
- from n=3 to n=1
- from n=4 to n=1
- from n=5 to n=1
- from n=6 to n=1

Therefore, there are 5 possible energy level transitions and hence 5 spectral lines emitted.

Therefore, the answer is (d) 3.