According to the periodic table, how many electrons does gallium (#31) have in its valence level? 3 13 31 2

Option A: 3

The atomic number of gallium atom is 31. It belongs to 13th group and 4th period of the periodic table.

The electronic configuration is as follows:

Here, Ar is the nearest noble gas.

The outermost electronic shells are

From the electronic configuration, valence electrons of  gallium are 3.

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%