Answer:
Cr3+ is green and V2+ is purple. Cr3+ and V2+ are both d3 so there can be a lot of movement between energy levels to produce colored light. Cd2+ and Hg2+ are both d10 (full d orbital, much less electron movement).
Explanation:
When going down a group the no of orbits increases. That is n value increases (n=principle quantum number). When the number of atomic orbitals increases, the radius gradually increases. (going down the group means the number of obits that electrons can fill will increase)
And the atomic radius from left to right in the periodic table actually DECREASES. That is due to increase in electronegetivity to the right side of the periodic table.
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The answer is (3) 3. The outer shell of an atom is called valence shell. And the ground state is the lowest energy state of an atom. Aluminum has a electron distribution of 2, 8, 3. So the outer shell has 3 electrons.