Atomic Structure

Step 1: Understanding the diffraction condition.
In x-ray diffraction, the observed peaks correspond to diffraction conditions where the diffraction condition is satisfied. For an fcc structure with two atoms in the basis, the allowed diffraction peaks occur when is an even number, and the peak satisfies this condition.
Step 2: Conclusion.
Therefore, the correct answer is option (C) because is the allowed peak.

Step 1: Understanding the Rydberg series.
Rydberg atoms are highly excited hydrogen-like atoms with large values of . When the atom transitions between adjacent energy levels, the emitted radiation lies in the ultraviolet (UV) range, with wavelengths on the order of nanometers ( ).
Step 2: Conclusion.
Therefore, the correct answer is option (B), as the radiation lies in the UV range.

Step 1: Write the Bohr model expression.
Kinetic energy of electron in a Bohr orbit: .

Step 2: Identify the energy levels.
Ground state: ⇒ .
Third excited state: ⇒ .

Step 3: Compute the ratio.
.

Step 4: Conclusion.
Thus, .