Periodicity Quick Kit: 17 MCQs with answers

F < O < N < C < B < Be < Li

Across a period, atomic radius decreases due to increasing effective nuclear charge, so F has the smallest radius and Li the largest.

F

Fluorine is the most electronegative element on the Pauling scale (3.98).

Na

Sodium (Na) is in Group 1, making it an alkali metal. K is also an alkali metal, but since only one answer is correct, Na is the correct choice.

Te

Atomic radius increases down a group. Among O, S, Se, Te, Te is the lowest in the group and thus has the largest atomic radius.

P < S < Cl

Non-metallic character increases across a period, so P (Group 15) is least non-metallic, followed by S, then Cl.

K < Na < Li

Electronegativity decreases down a group, so K has the lowest electronegativity, followed by Na, then Li.

False

Fluorine has the highest electronegativity (3.98), not chlorine.

True

Down a group, the number of shells increases, so the atomic radius increases.

Ne

Ionization enthalpy generally increases across a period. Ne, being a noble gas with a stable octet, has the highest first ionization enthalpy in the second period.

Cl > F > Br > I

Chlorine has the most negative electron gain enthalpy among halogens because of its smaller size and effective nuclear charge; fluorine's small size causes electron-electron repulsion, making its electron gain enthalpy less negative than chlorine.

Al < Mg < Na

Metallic character decreases across a period, so Na (Group 1) is most metallic, followed by Mg, then Al.

S > O > Se > Te

Electron gain enthalpy becomes more negative down a group, but oxygen is an exception due to its small size and electron-electron repulsion. Thus, S has the most negative electron gain enthalpy among these.

F < O < N

Valence generally increases up to group 15 and then decreases. For N (group 15) valence is 3, O (group 16) valence is 2, F (group 17) valence is 1. So the order is F < O < N.

Na < Al < Mg

Ionization enthalpy increases across a period, but there is a dip at Al because it has a single p electron, which is easier to remove than the paired s electron in Mg. So the order is Na < Al < Mg.

Li and Mg

A diagonal relationship is observed between Li-Mg, Be-Al, and B-Si. The question asks for one, so Li and Mg is correct.

B < C < O < N

Ionization enthalpy generally increases across a period, but there is a dip at O due to the extra stability of half-filled p orbitals in N. So the order is B < C < O < N.

Al3+ < Mg2+ < Na+

Cations are smaller than their parent atoms. Among isoelectronic ions, the one with the highest positive charge has the smallest radius. So Al3+ < Mg2+ < Na+.