Chemistry - PERIODIC TABLE Question with Solution | TestHub

The question asks to identify the option where the property first increases and then decreases when moving from left to right among the given elements.

Option A: Al, Ga (Electronegativity)

Electronegativity generally decreases down a group. However, due to poor shielding by d-electrons, Ga is slightly more electronegative than Al. The trend is Al (1.61) < Ga (1.81). This is an increasing trend.

Option B: O, S, Se (Electron affinity)

Electron affinity generally decreases down a group. However, due to small size and interelectronic repulsion, oxygen has a lower electron affinity than sulfur. The trend is O (-141 kJ/mol) < S (-200 kJ/mol) > Se (-195 kJ/mol). This shows an increase then a decrease.

Option C: O, N, F (Ionization energy)

Ionization energy generally increases across a period. However, nitrogen has a higher ionization energy than oxygen due to its stable half-filled p-subshell. The trend is N (1402 kJ/mol) > O (1314 kJ/mol) < F (1681 kJ/mol). This shows a decrease then an increase.

Option D: Mn, Cr, V (Spin magnetic moment) Spin magnetic moment is proportional to the number of unpaired electrons.

V: $[Ar]3d^{3}4s^2$, 3 unpaired electrons.

Cr: $[Ar]3d^{5}4s^1$, 6 unpaired electrons.

Mn: $[Ar]3d^{5}4s^2$, 5 unpaired electrons. The number of unpaired electrons is V (3) < Cr (6) > Mn (5). This shows an increase then a decrease.

Therefore, options B and D show the described trend.

The final answer is $\boxed{B,D}$.