Periodic Trends — Set 2

Correct Answer: A. Newlands

• **Newlands law** = John Newlands proposed the law of octaves in 1864 based on element arrangements. • **Musical analogy** — He noted every eighth element had similar properties to the first (like musical octaves). • 💡 Wrong-option analysis: B: Dobereiner proposed triads; C: Mendeleev created periodic table; D: Moseley determined atomic numbers.

Correct Answer: C. f-block

• **f-block metals** = The f-block, containing lanthanides and actinides, has only metallic elements. • **Inner transition** — These elements are called inner transition elements or rare earths. • 💡 Wrong-option analysis: A: p-block has nonmetals too; B: d-block has nonmetals; D: s-block has hydrogen.

Correct Answer: B. Atomic Radius

• **Radius increase** = Atomic radius increases down a group as new electron shells are added. • **Shielding effect** — Outer electrons are farther from nucleus, resulting in larger atoms. • 💡 Wrong-option analysis: A: Electronegativity decreases; C: Non-metallic character decreases; D: Ionization energy decreases.

Correct Answer: C. Lithium

• **Lithium lightness** = Lithium is the lightest metal and the least dense solid element overall. • **Low density** — Its density is lower than water, making it float on water surfaces. • 💡 Wrong-option analysis: A: Hydrogen is nonmetal; B: Beryllium is denser; D: Sodium is denser.

Correct Answer: B. Dmitri Mendeleev

• **Mendeleev credit** = Dmitri Mendeleev created the first widely recognized and accepted periodic table. • **Predictions made** — He accurately predicted properties of undiscovered elements, validating his arrangement. • 💡 Wrong-option analysis: A: Meyer contributed independently; C: Dalton developed atomic theory; D: Moseley refined by atomic number.

Correct Answer: D. Group 18

• **Noble gases** = Group 18 elements (noble gases) are chemically inert with complete electron shells. • **Stable configuration** — Having eight valence electrons (except helium with two), they don't need to react. • 💡 Wrong-option analysis: A: Group 1 are highly reactive; B: Group 17 are very reactive; C: Group 2 are quite reactive.

Correct Answer: D. Period 2 and 3

• **Period 2-3 relationship** = Diagonal relationship exists between certain elements of periods 2 and 3. • **Similar sizes** — Elements like lithium-magnesium and beryllium-aluminum have similar properties due to size and charge. • 💡 Wrong-option analysis: A: No diagonal between 3 and 4; B: Diagonal isn't group-based; C: No diagonal between 1 and 2.

Correct Answer: D. Gallium

• **Gallium prediction** = Gallium was predicted by Mendeleev as 'Eka-aluminum' based on periodic table position. • **Accurate forecast** — Its actual properties matched Mendeleev's predictions remarkably closely after discovery. • 💡 Wrong-option analysis: A: Scandium wasn't predicted with that name; B: Silicon was known; C: Germanium had different predictions.

Correct Answer: A. +2

• **Group 2 valency** = Group 2 elements (alkaline earth metals) have two valence electrons, giving +2 charge. • **Stable ion** — They lose both valence electrons to achieve stable noble gas configuration. • 💡 Wrong-option analysis: B: Group 1 is +1; C: Nonmetal would have negative; D: Group 13 is +3.

Correct Answer: D. Mercury

• **Mercury liquid** = Mercury is the only metal remaining liquid at standard room temperature and pressure. • **Low melting** — Its melting point is -39°C, well below room temperature (25°C). • 💡 Wrong-option analysis: A: Gallium melts at 29.8°C, near room temperature; B: Chlorine is gas; C: Phosphorus is solid.