Their Period number is common means their "Principal Quantum Numbers" are same
Hope this helps!
Removing an electron from a neutral atom will result in an atom that is positive.
Oxygen is a gas a room temperature.
You should trust the primary source more.
This is because the primary source is make its conclusion from direct observation, while the secondary source is possibly making reference to another secondary source or to another primary.
The primary source should be trusted more because it is from direct observation.
