1. Which element has the highest 2nd Ionization Enthalpy: Na, Mg, Al, Si?
+
Correct Answer
Na
Detailed Explanation
The second ionization enthalpy (IE2) is the energy
required to remove the second electron from a gaseous unipositive ion:
M+(g) → M2+(g) + e−
The key is to examine the electronic configuration after the first
electron has already been removed.
Na (Z = 11): 1s2 2s2 2p6 3s1
After first ionization:
Na+ = 1s2 2s2 2p6
= [Ne]
Now the second electron must be removed from a completely filled
noble-gas shell. Therefore, an exceptionally large amount of energy
is required.
For comparison:
Mg → Mg+ = [Ne]3s1
So the second electron of Mg is still a 3s valence electron
and is comparatively easier to remove.
Similarly:
Al+ = [Ne]3s2
and
Si+ = [Ne]3s23p1
Their second electrons are removed from the outer shell rather than from a
stable noble-gas core.
Therefore:
IE2(Na) ≫ IE2(Mg), IE2(Al), IE2(Si)
Hence, Na has the highest second ionization enthalpy.
JEE Shortcut
Whenever an ionization-energy question asks for the nth ionization
enthalpy, check whether the previous ionization has produced a
noble-gas configuration.
For Na:
Na → Na+ = [Ne]
Therefore:
Na+ → Na2+ + e−}
requires removal of a core electron, causing a huge jump in
energy.
Rule: Removal of an electron from a noble-gas configuration
requires exceptionally high ionization enthalpy.
30 Related MCQs with Solutions
1. Which element has the highest second ionization enthalpy among Na, Mg, Al and Si?
A. Na
B. Mg
C. Al
D. Si
Answer: A. Na
Na+ has the stable [Ne] configuration.
Na+ has the stable [Ne] configuration.
2. The second ionization process is:
A. M → M+ + e−
B. M+ → M2+ + e−
C. M2+ → M3+ + e−
D. M− → M + e−
Answer: B
3. Na+ has the electronic configuration:
A. [Ne]
B. [Ar]
C. [He]
D. [Kr]
Answer: A. [Ne]
4. The second electron of Na is removed from:
A. 3s orbital
B. 3p orbital
C. 2p orbital
D. 1s orbital
Answer: C. 2p orbital
After Na loses its 3s electron, the next electron comes from the [Ne] core.
After Na loses its 3s electron, the next electron comes from the [Ne] core.
5. Which ion has a noble-gas configuration?
A. Na+
B. Mg+
C. Al+
D. Si+
Answer: A. Na+
6. Which generally shows a very large jump between IE1 and IE2?
A. Na
B. Mg
C. Al
D. Si
Answer: A. Na
7. For Mg, the first ionization produces:
A. [Ne]3s1
B. [Ne]
C. [Ne]3p1
D. [Ar]
Answer: A. [Ne]3s1
8. Which element has a filled 3s subshell in its neutral state?
A. Na
B. Mg
C. Al
D. Si
Answer: B. Mg
9. Al has the configuration:
A. [Ne]3s23p1
B. [Ne]3s1
C. [Ne]3p2
D. [Ar]3s1
Answer: A
10. Si+ has:
A. [Ne]3s23p1
B. [Ne]3s2
C. [Ne]3s1
D. [Ar]
Answer: A
11. The largest jump in successive ionization enthalpies occurs when:
A. A core electron starts being removed
B. A valence electron is removed
C. Atomic size increases
D. Neutron number changes
Answer: A
12. The exceptionally high IE2 of Na is due to:
A. Large atomic size
B. Removal of a core electron from [Ne]
C. Low nuclear charge
D. Addition of an electron
Answer: B
13. Which species is most difficult to ionize further?
A. Na+
B. Mg+
C. Al+
D. Si+
Answer: A. Na+
14. Which has a closed-shell configuration after first ionization?
A. Na
B. Mg
C. Al
D. Si
Answer: A. Na
15. Which electron is removed first from Na?
A. 1s
B. 2p
C. 3s
D. 3p
Answer: C. 3s
16. The electronic configuration of Na is:
A. [Ne]3s1
B. [Ne]3s2
C. [Ar]3s1
D. [He]2s1
Answer: A
17. Which element belongs to Group 1 among the options?
A. Na
B. Mg
C. Al
D. Si
Answer: A. Na
18. A huge IE2 generally indicates that M+ has:
A. A noble-gas configuration
B. One valence electron
C. An unpaired p electron
D. A large atomic radius
Answer: A
19. Which ion is isoelectronic with Ne?
A. Na+
B. K+
C. Ca2+
D. Cl−
Answer: A. Na+
20. Which factor makes removal of a core electron difficult?
A. Strong nuclear attraction
B. Large distance from nucleus
C. Weak shielding only
D. Low nuclear charge
Answer: A
21. Which has the highest IE2 among the following?
A. Li
B. Be
C. B
D. C
Answer: A. Li
Li+ has the [He] configuration.
Li+ has the [He] configuration.
22. Which element shows a large jump after IE1?
A. Na
B. Mg
C. Al
D. Si
Answer: A. Na
23. For Mg, the second ionization removes the:
A. 3s electron
B. 2p electron
C. 1s electron
D. 3p electron
Answer: A. 3s electron
24. For Na, the second ionization removes a:
A. Valence electron
B. Core electron
C. 3s electron
D. 3p electron
Answer: B. Core electron
25. Which configuration is most stable?
A. [Ne]3s1
B. [Ne]
C. [Ne]3s23p1
D. [Ne]3s2
Answer: B. [Ne]
26. The first four elements of the third period are:
A. Na, Mg, Al, Si
B. Li, Be, B, C
C. K, Ca, Sc, Ti
D. F, Ne, Na, Mg
Answer: A
27. Which statement is correct?
A. IE2 of Na is exceptionally high
B. IE2 of Na is lower than IE1
C. Na+ has one valence electron
D. Na+ is not stable
Answer: A
28. The noble-gas configuration of Na+ is:
A. [He]
B. [Ne]
C. [Ar]
D. [Kr]
Answer: B. [Ne]
29. The main factor responsible for exceptionally high second IE of Na is:
A. Core-electron removal
B. Large atomic radius
C. Low effective nuclear charge
D. Electron-electron repulsion
Answer: A
30. The correct conclusion for Na, Mg, Al and Si is:
A. Na has the highest IE2
B. Mg has the highest IE2
C. Al has the highest IE2
D. Si has the highest IE2
Answer: A. Na
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