Question

which atom/ion is the smallest?
a) se²-
b) br-
c) rb+
d) y³+
e) mo⁶+

Explanation:

When comparing the size of isoelectronic species (species with the same number of electrons), the ion with the highest positive charge (most protons in the nucleus) will have the smallest radius. This is because a higher positive charge exerts a stronger pull on the electrons, pulling them closer to the nucleus.

• \(Se^{2 -}\) has a relatively low positive charge compared to the others.
• \(Br^{-}\) also has a negative charge, so the nuclear pull is not as strong as in positive ions.
• \(Rb^{+}\) has a +1 charge.
• \(Y^{3+}\) has a +3 charge.
• \(Mo^{6+}\) has the highest positive charge (+6) among the given ions. With more protons in the nucleus (for isoelectronic species), it will attract the electrons most strongly, resulting in the smallest radius.

Answer:

E. \(Mo^{6+}\)