JEE Main 2020 — Chemistry Physical Chemistry

2020mcqhard

Consider the hypothetical situation where the azimuthal quantum number, $l$ , takes values $0,1,2,\ldots \ldots ..n+1$ . Where n is the principal quantum number. Then, the element with atomic number:

Official previous-year question

Held on 3 Sept 2020 · Verified 6 Jul 2026.

Options

A
9 is the first alkali metal
B
13 has a half-filled valence subshell
C
8 is the first noble gas
D
6 has a 2p-valence subshell

Did you get this right?

Solution

For $n=1$ value of $l=0,1,2$

For $n=2$ value of $l=0,1,2,3$

So, according to $n+l$ rule the filling order of subshells will be :

$1s1p2s1d2p3s2d3p4s.....$

(1) ${1}^{\mathrm{st}}$ alkali metal will have configuration $1{s}^{2}1{p}^{6}$ so atomic number will be $8$ .

(2) ${1}^{\mathrm{st}}$ alkali metal will have electronic configuration $\Rightarrow 1{s}^{1}\Rightarrow (Z=1)$

(3) Electronic configuration of $C(Z=6)\Rightarrow 1{s}^{2}1{p}^{4}$

(4) $Z=13$ , Electronic configuration $=1{s}^{2}1{p}^{6}2{s}^{2}1{d}^{3}$

So it will not have half-filled electronic configuration.

Your note

JEE Main Physical Chemistry in other years

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Work through every JEE Main Physical Chemistry PYQ, year by year.

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JEE Main 2020 — Chemistry Physical Chemistry

2020mcqhard

Consider the hypothetical situation where the azimuthal quantum number, $l$ , takes values $0,1,2,\ldots \ldots ..n+1$ . Where n is the principal quantum number. Then, the element with atomic number:

Official previous-year question

Held on 3 Sept 2020 · Verified 6 Jul 2026.

Options

A
9 is the first alkali metal
B
13 has a half-filled valence subshell
C
8 is the first noble gas
D
6 has a 2p-valence subshell

Did you get this right?

Solution

For $n=1$ value of $l=0,1,2$

For $n=2$ value of $l=0,1,2,3$

So, according to $n+l$ rule the filling order of subshells will be :

$1s1p2s1d2p3s2d3p4s.....$

(1) ${1}^{\mathrm{st}}$ alkali metal will have configuration $1{s}^{2}1{p}^{6}$ so atomic number will be $8$ .

(2) ${1}^{\mathrm{st}}$ alkali metal will have electronic configuration $\Rightarrow 1{s}^{1}\Rightarrow (Z=1)$

(3) Electronic configuration of $C(Z=6)\Rightarrow 1{s}^{2}1{p}^{4}$

(4) $Z=13$ , Electronic configuration $=1{s}^{2}1{p}^{6}2{s}^{2}1{d}^{3}$

So it will not have half-filled electronic configuration.

Your note

JEE Main Physical Chemistry in other years

Keep practicing Physical Chemistry

Work through every JEE Main Physical Chemistry PYQ, year by year.

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JEE Main 2020 — Chemistry Physical Chemistry

Options

Did you get this right?

Solution

Your note

JEE Main Physical Chemistry in other years

More JEE Main Physical Chemistry questions

Other Chemistry topics for JEE Main

Organic Chemistry

Inorganic Chemistry

Keep practicing Physical Chemistry

JEE Main 2020 — Chemistry Physical Chemistry

Options

Did you get this right?

Solution

Your note

JEE Main Physical Chemistry in other years

More JEE Main Physical Chemistry questions

Other Chemistry topics for JEE Main

Organic Chemistry

Inorganic Chemistry

Keep practicing Physical Chemistry