The correct trend in the first ionization enthalpies of the elements in the $3^{\text{rd}}$ period of periodic table is:

(A) $\mathrm{Al}<\mathrm{Si}<\mathrm{S}<\mathrm{P}<\mathrm{Cl}$

(B) $\mathrm{Al}<\mathrm{S}<\mathrm{P}<\mathrm{Si}<\mathrm{Cl}$

(C) $\mathrm{Si}<\mathrm{S}<\mathrm{Al}<\mathrm{P}<\mathrm{Cl}$

(D) $\mathrm{S}<\mathrm{Si}<\mathrm{Al}<\mathrm{P}<\mathrm{Cl}$

JEE Main · 2026 · 23 Jan 2026 · Shift 1 · Classification of Elements and Periodicity

The correct trend in the first ionization enthalpies of the elements in the

3^{rd}

period of periodic table is:

(A) $Al < Si < S < P < Cl$ ✓ Correct
(B) $Al < S < P < Si < Cl$
(C) $Si < S < Al < P < Cl$
(D) $S < Si < Al < P < Cl$

Answer: (A)

Solution

Across the third period the first ionisation enthalpy generally rises with increasing effective nuclear charge, but with two breaks. Aluminium loses an electron from a higher-energy

3 p

orbital and so lies below silicon. Phosphorus has an extra-stable half-filled

3 p^{3}

configuration and resists ionisation more than sulphur, so sulphur lies below phosphorus. Putting these together, the increasing order is

Al < Si < S < P < Cl

JEE Main · 2026 · 23 Jan 2026 · Shift 1 · Single correct option

Practise more: all JEE Main PYQs on Classification of Elements and Periodicity →

More JEE Main questions on Classification of Elements and Periodicity

Which of the following represents the correct trend for the mentioned property?
A. $F > P > S > B$ - First Ionization Energy
B. $Cl > F > S > P$ - Electron Affinity
C. …
JEE Main 2026View solution →
Given below are two statements:

Statement-I: The correct order in terms of atomic/ionic radii is $Al > Mg > Mg^{2 +} > Al^{3 +}$ .

Statement-II: The correct order in terms of the magnitude of electron gain enthalpy is …
JEE Main 2026View solution →
Given below are two statements :

Statement-I : The first ionization enthalpy of Cr is lower than that of Mn.
Statement-II : The second and third ionization enthalpies of Cr are higher than those of Mn .

In the light of the above statements, choose the correct answer from the op …
JEE Main 2026View solution →
Given below are two statements :

Statement-I : $C < O < N < F$ is the correct order in terms of first ionization enthalpy values.

Statement-II : $S > Se > Te > Po > O$ is the correct order in terms of the ma …
JEE Main 2026View solution →
The correct statements from the following are :
(A) Ionic radii of trivalent cations of group 13 elements decreases down the group.
(B) Electronegativity of group 13 elements decreases down the group.
(C) Among the group 13 elements, Boron has highest first ionisation enthalpy.
( …
JEE Main 2026View solution →
Elements X and Y belong to Group 15. The difference between the electronegativity values of 'X' and phosphorus is higher than that of the difference between phosphorus and 'Y'. 'X' & 'Y' are respectively
JEE Main 2026View solution →