The following ions contain the same number of electrons. Rank them in order of decreasing ionic radii. Rank from largest to smallest radius. To rank items as equivalent, overlap them. se3+ cl-

Cl- < Se3+ is the decreasing order of ionic radii of the two ions.

Explanation:

Atomic number of Se= 34 Se3+ will have 31 electrons (+ sign indicates loss of electron)

Atomic number of chlorine is 17, Cl- will have 18 electrons (- sign shows gain of electrons)

Number of electrons in their valence shell:

Se3+ = 2,8,18,3

Cl- = 2,8,8

The Se3+ atoms have K.L.M.N shells while Cl- K,L,M shells

The size of the ions is based on the effective nuclear charge on the ion. The loss in electron causes small cation and gain in electron causes increase in anion size.

The number of occupied shells more the number more is the ionic radii.

Se3+ will have large ionic radii as Se+ has four filled shells.

Cl- < Se3+ (decreasing order of ionic radii)

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the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.