Identify the isoelectronic elements. i. Cl-, F-, Br-, I-, At-
ii. Ne, Ar, Kr, Xe, He
iii. N3-, S2-, Br-, Cs+, Sr2+
iv. N3-, O2-, F-, Na+, Mg2+
v. Li+, Na+, K+, Rb+,Cs+

iv. N³⁻, O²⁻, F⁻, Na⁺, Mg²⁺

Explanation:

Isoelectronic elements are those that have the same number of electrons. So, if at least 2 elements differ in their number of electrons, the series is not of isoelectronic elements.

To know the number of electrons we will consider the atomic number and add electrons if it is an anion and subtract electrons it is a cation.

Identify the isoelectronic elements.

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%

thats a little if u want the answer just look it up on google thats what i do haha : )