The gravitational force between a $H$-atom and another particle of mass $m$ is given by Newton's law $F = G\frac{M m}{r^2}$. Here,$M$ represents:

• A
  $M = m_{proton} + m_{electron}$
• B
  $M = m_{proton} + m_{electron} - \frac{B}{c^2}$ (where $B = 13.6 \, eV$)
• C
  $M$ is not related to the mass of the hydrogen atom
• D
  $M = m_{proton} + m_{electron} - \frac{|V|}{c^2}$ (where $|V|$ is the magnitude of potential energy)