You have a vial that may contain lead(II) cations or barium cations, but not both. Available to you are solutions of ammonium sulfate, sodium fluoride and potassium bromide. Which single solution can you add to the vial to determine which cation is present?

We should add, the KBr solution.

Explanation:

The vial contains Ba²⁺  and Pb²⁺

Our solutions are: (NH₄)₂ SO₄, NaF and KBr

We dissociate the solutions:

(NH₄)₂ SO₄  → 2NH₄⁺ + SO₄⁻²

NaF → Na⁺ + F⁻

KBr → K⁺ + Br-

When we add ammonium sulfate and sodium fluorine, we are adding sulfates and fluorines, but these two anions make precipitate both cations, we can not determine, if the vial contains Ba²⁺ or Pb²⁺

SO₄⁻²(aq) + Ba²⁺ (aq) → BaSO₄ (s)  ↓

SO₄⁻² (aq)+ Pb²⁺(aq)  → PbSO₄ (s)  ↓

2F⁻ (aq) + Ba²⁺ (aq) → BaF₂ (s) ↓

2F⁻ (aq) + Pb²⁺ (aq) → PbF₂ (s)  ↓

When we add the KBr, bromides only make precipitate with Pb²⁺, so the vial has only Pb²⁺ cation:

2Br⁻ (aq) + Ba²⁺ (aq) → BaBr₂ (aq)

2Br⁻ (aq) + Pb²⁺ (aq) → PbBr₂ (s) ↓

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."

considering the question as per the attachment

here we can see that the radon nuclide has 222 as the atomic mass number and 86 as the atomic number.

when it undergoes nuclear fission it gives polonium which has atomic mass number as 218 and atomic number will be 84 along with a helium nucleus which has 4 atomic mass number and 2 as its atomic number.

222 = 218 + 4 (atomic mass number)

86 = ? + 2; therefore ? = 86-2 = 84.

the atomic mass number of polonium will be 84.