Imagine an atom made up of a proton and a hypothetical particle of double the mass as that of an electron but the same charge. Apply Bohr theory to consider transitions of the hypothetical particle to the ground state. Then, the longest wavelength (in terms of Rydberg constant for hydrogen atom) is

A

$$\frac{1}{2R}$$

B

$$\frac{5}{3R}$$

C

$$\frac{1}{3R}$$

D

$$\frac{2}{3R}$$