Question

In which energy level is the outer electron in rubidium located?
A. 85
B. 2
C. 37
D. 1
E. 5

Answer 1

For solving this question, first we need to understand the concepts of the line spectrum of Hydrogen. We can state that when hydrogen gas at low pressure is taken in a discharged tube then the light emitted is passed through an electric charge which is examined with a spectroscope. Thus, the spectrum obtained is known as the line spectrum of hydrogen.

Complete step by step answer: We can define energy levels as the fixed distance from the nucleus of an atom where electrons are found. When the number of protons present in the nucleus increases then we move from right to left in the periodic table. In the periodic table, each row represents an energy level. Thus, the elements present in each column share similar properties and the same number of valence electrons. So, we can define valence electrons as the number of electrons present in the outermost energy level.
So, according to the question, rubidium Rb has an atomic number of 37. Then, based on the atomic number of Rb i.e. 37 we will write the electron configuration:
$1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^2}3{d^{10}}4{p^6}5{s^1}$.
By referring to the electronic configuration of Rb the outermost electron lies in 5th energy level.

Therefore, the option E is correct.

Note: When we talk about Rubidium we need to know that it is soft, silvery-white metal present in the alkali metal group. Rubidium metal shares similarities with the Potassium metal and to the Caesium metal in case of physical appearance, conductivity and softness. Also, it is used in vacuum tubes as a material that combines and removes traces of gas from the vacuum tubes. It can also be used in manufacturing photocells and glasses.