an aluminum atom will lose the 3 electrons on its outer shell 2 for an aluminum ion.
It will lose 2 to form Sr2+
Krypton is a noble gas and generally does not gain or lose electrons.
In phosphene it gain 4 electrons. Phosphate lose 4 electrons
Because Sodium is in group 1, it tends to lose one electron when forming an ion, therefore having a charge of +1