How can I determine the quantum number of a electron lost during ion formation? How do quantum numbers change for ions?


  A sample question: Give the set of four quantum numbers that could represent the electron lost to form the Rb ION from the Rb atom. 


The answer given is $n=5; l=0; m_l=0; m_s= +\frac12$. I chose the answer: $n=4; l=1; m_l=1; m_s= -\frac12$. 

I am looking for an explanation. I am confused because I thought the question asked me to describe $\ce{Rb+}$ and the answer given is the same that I would choose for $\ce{Rb}$ at ground state. If it is asking me to describe the electron, how is that technically possible if I don't know where the electron went? Sounds silly and I know I'm over thinking it. Some insight would be appreciated.
The correct answer has been given in the comments section of this post. I am providing the answer here in accordance with a meta post discussion.

The question you were asked was in reference to the quantum numbers that correspond to the electron lost when $\ce{Rb}$ goes to $\ce{Rb+}$. The electronic configuration of $\ce{Rb}$ is $[\ce{Kr}]\ 5\mathrm{s}^{1}$; thus, you need the set of quantum numbers for a $5\mathrm{s}^{1}$ electron. That set of quantum numbers is: 

$$n = 5;\ l= 0;\ m_{l} = 0;\ m_{s} = +{1\over2}$$