Answer:
There are 13 electrons in atom of aluminium and 34 in atom of selenium.
Step-by-step explanation:
Aluminium:
It is present in group 13.
It has three valance electrons.
It form cation.
Its electronic configuration is:
Al = [Ne] 3s² 3p¹
The electron in 3s and 3p are considered as valance electrons of aluminium.
Aluminium atom has 13 protons and 14 neutrons thus its mass number is 27 amu.
Selenium:
It is present in group 16.
It has six valance electrons.
It form anion.
Its electronic configuration is:
Se = [Ar] 3d¹⁰ 4s² 4p⁴
The electron in 4s and 4p are considered as valance electrons of selenium.
Selenium atom has 34 protons and 45 neutrons thus its mass number is 79 amu.