<u>Answer:</u>
Ion is a charged particle.
A neutral atom contains equal number of positive protons and negative electrons
When an electron is lost or gained the atom becomes a charged particle which is called as an ION.
For example
Na is an atom which contains 11 electrons and 11 protons (= to atomic number)
When Na loses an electron it will have 11 positive proton and 10 negative electron and Thus, Na will become , a charge particle which we call it as sodium ion.
Cl is an atom which contains 17 electrons and 17 protons (= to atomic number)
When Cl loses an electron it will have 17 positive proton and 18 negative electron and Thus, Cl will become , a charge particle which we call it as chloride ion.
When an ion is positively charged it is called as a cation
When an ion is negatively charged it is called as an anion.
Beryllium forms cation.we see this in Beryllium chloride .
If is present in water it forms Beryllium ions which is in Hydrated form that is molecules are present in its ion .