Which ion does not have a noble gas configuration in its ground state? which ion does not have a noble gas configuration in its ground state? al3+ sc3+ as3- ga3+?

The correct answer is Ga3+.  

Electron configuration of Al is [Ne] 3s2 3p1  

Electron configuration of Al3+ is [Ne]  

So the electron configuration of Al3+ is like that of Ne.  

Electron configuration of Sc is [Ar] 3d1 4s2  

Electron configuration of Sc3+ is [Ar]  

So the electron configuration of Sc3+ is like that of Ar.  

Electron configuration of As is [Ar] 3d10 4s2 4p3  

Electron configuration of As3- is [Ar] 3d10 4s2 4p6

So the electron configuration of As3- is like that of Kr

Electron configuration of Kr [Ar] 3d10 4s2 4p6  

Electron configuration of Ga is [Ar] 3d10 4s2 4p1

Electron configuration of Ga3+ is [Ar]3d10

The presence of the ten d orbital electrons prevents Ga3+ from having the same electron configuration as Argon.  

All other choices have the same electron configurations as a noble gas.  

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%