Periodic Trends — Set 5

Correct Answer: B. Sulfuric acid

• **Sulfuric acid** = Sulfuric acid is called the 'King of Chemicals' due to highest industrial production. • **Wide applications** — Used in numerous industries including fertilizers, refining, and manufacturing. • 💡 Wrong-option analysis: A: Oxygen is important but not titled so; C: Chlorine is important but different title; D: Sodium chloride is different.

Correct Answer: C. No clear trend

• **Irregular melting** = Melting points across a period show no clear continuous trend due to bonding changes. • **Type variation** — Transition from metallic to ionic to covalent to molecular bonding causes variation. • 💡 Wrong-option analysis: A: Metals high, then decreases for nonmetals; B: Not consistent; D: Definitely changes.

Correct Answer: C. Fluorine

• **Fluorine reactivity** = Fluorine is the most reactive nonmetal in the periodic table. • **Extreme reactivity** — It reacts with almost all elements and even noble gases under certain conditions. • 💡 Wrong-option analysis: A: Oxygen is reactive but less; B: Chlorine is reactive but less; D: Bromine is much less reactive.

Correct Answer: B. Incomplete shielding by f-electrons

• **Incomplete shielding** = Lanthanide contraction results from poor shielding by f-electrons. • **Atomic size decrease** — Despite added electrons, atomic size decreases due to poor shielding effect. • 💡 Wrong-option analysis: A: Electrons aren't lost; C: Atomic number increases but doesn't cause contraction; D: Stability isn't the cause.

Correct Answer: A. 10

• **d-orbital capacity** = d-orbitals can hold maximum 10 electrons (5 d-orbitals × 2 electrons each). • **Orbital structure** — Five d-orbitals allow pairing of up to 10 electrons total. • 💡 Wrong-option analysis: B: 14 is for f-orbitals; C: 6 is for p-orbitals; D: 2 is for s-orbital.

Correct Answer: B. Manganese

• **Manganese oxidation** = Manganese shows the maximum number of oxidation states (+2 to +7) among transition metals. • **Variable states** — Its electron configuration allows diverse oxidation state possibilities. • 💡 Wrong-option analysis: A: Iron shows fewer states; C: Copper shows fewer states; D: Zinc usually shows +2 only.

Correct Answer: B. One valence electron

• **Hydrogen valency** = Hydrogen is placed at Group 1 top because it has one valence electron like alkali metals. • **Similar behavior** — Under extreme pressure, hydrogen shows metallic properties similar to alkali metals. • 💡 Wrong-option analysis: A: Abundance doesn't determine placement; C: Atomic mass doesn't determine placement; D: Based on chemical properties.

Correct Answer: B. Horizontal arrangement

• **Period definition** = Period refers to horizontal arrangement of elements in the periodic table. • **Electron shells** — Each period corresponds to elements with the same number of electron shells. • 💡 Wrong-option analysis: A: Vertical arrangement is groups; C: Blocks don't follow periods exactly; D: Valency is in groups.

Correct Answer: B. Atomic number

• **Atomic number basis** = Elements are arranged by atomic number (number of protons) in modern periodic table. • **Moseley's discovery** — Henry Moseley's X-ray experiments proved atomic number better than atomic mass. • 💡 Wrong-option analysis: A: Mendeleev used this; C: Used to predict properties; D: Used to predict properties.

Correct Answer: B. They have similar valence electrons

• **Group similarity** = Elements in the same group have the same number of valence electrons. • **Similar chemistry** — This commonality explains their similar chemical properties and reactions. • 💡 Wrong-option analysis: A: Valence electrons are same; C: Atomic numbers differ; D: Atomic masses differ.