Atomic Structure, Isotopes, Ions and Electronic Configuration

1. An atom of element X has proton number 13 and nucleon number 27.

Which row is correct?

	number of protons	number of neutrons	number of electrons
A	13	14	13
B	14	13	13
C	13	27	14
D	27	13	13

2. An ion Y2– has 18 electrons and 16 neutrons.

What is the nucleon number of atom Y?

A 16
B 18
C 32
D 34

3. Which particle contains 10 electrons?

A Na
B Na+
C Mg
D F

4. An atom has electronic configuration 2,8,7.

Which ion is it most likely to form?

A 1+
B 1–
C 7+
D 7–

5. Which pair represents isotopes of the same element?

	protons	neutrons	electrons
W	17	18	17
X	17	20	17
Y	18	17	18
Z	16	20	18

A W and X
B W and Y
C X and Z
D Y and Z

6. An ion has electronic configuration 2,8. It has a 2+ charge.

What is the electronic configuration of the neutral atom?

A 2,6
B 2,8
C 2,8,2
D 2,8,8

7. Element Q forms an ion Q3+ with electronic configuration 2,8.

Where is Q found in the Periodic Table?

A Group III, Period 2
B Group III, Period 3
C Group V, Period 2
D Group V, Period 3

8. An atom contains 12 protons, 12 neutrons and 12 electrons.

Which statement is correct?

A It has nucleon number 12.
B It has atomic number 24.
C It forms a 2+ ion by losing two electrons.
D It forms a 2– ion by gaining two electrons.

9. Which statement about isotopes is correct?

A They have the same number of neutrons but different numbers of protons.
B They have the same number of protons but different numbers of neutrons.
C They have the same nucleon number but different proton numbers.
D They have different chemical properties because they have different masses.

10. Naturally occurring chlorine contains 75% chlorine-35 and 25% chlorine-37.

What is the relative atomic mass of chlorine?

A 35.0
B 35.5
C 36.0
D 37.0

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

11. The relative atomic mass of element X is 63.5. X has two isotopes, X-63 and X-65.

What are the approximate percentages of X-63 and X-65?

	X-63	X-65
A	25%	75%
B	50%	50%
C	75%	25%
D	100%	0%

12. Which ion has the same electronic configuration as neon?

A Cl–
B O2–
C K+
D Ca2+

13. Which particles are both anions?

A Mg2+ and Al3+
B Na+ and F–
C O2– and Cl–
D NH4+ and SO4 2–

14. An atom of element Z has 3 occupied electron shells and 6 electrons in its outer shell.

Which statement is correct?

A Z is in Group VI and Period 3.
B Z is in Group III and Period 6.
C Z is in Group VI and Period 6.
D Z is in Group III and Period 3.

15. A particle has 19 protons, 20 neutrons and 18 electrons.

Which symbol represents the particle?

A 39K+
B 39K–
C 39Ar+
D 20K+

16. Which statement about a proton is correct?

A It has a relative charge of –1 and relative mass of 1.
B It has a relative charge of +1 and relative mass of 1.
C It has a relative charge of 0 and relative mass of 1.
D It has a relative charge of +1 and relative mass of 1/1840.

17. Which particle has the greatest number of electrons?

A Al3+
B Mg2+
C Na+
D S2–

18. Element R has electronic configuration 2,8,8,1.

Which statement is correct?

A R is a noble gas.
B R forms R+ by gaining one electron.
C R forms R+ by losing one electron.
D R forms R– by losing one electron.

19. Which atom has the largest number of occupied electron shells?

A 2,8,1
B 2,8,8
C 2,8,8,1
D 2,6

20. An ion X3– has electronic configuration 2,8.

What is the proton number of X?

A 7
B 10
C 13
D 15

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

21. Which row correctly describes the particles in an atom?

	proton	neutron	electron
A	nucleus	nucleus	shells
B	shells	nucleus	nucleus
C	nucleus	shells	shells
D	shells	shells	nucleus

22. Which statement about ions is correct?

A Positive ions have more electrons than protons.
B Negative ions have fewer electrons than protons.
C Positive ions form when atoms lose electrons.
D Negative ions form when atoms lose protons.

23. Element X has two isotopes.

Isotope 1 has relative mass 10 and percentage abundance 20%.
Isotope 2 has relative mass 11 and percentage abundance 80%.

What is the relative atomic mass of X?

A 10.2
B 10.5
C 10.8
D 11.0

24. Which two particles have the same number of electrons?

A F– and Mg2+
B Na and Na+
C Cl– and F–
D O2– and Cl–

25. An atom forms an ion by losing three electrons. The ion has 10 electrons.

What is the proton number of the atom?

A 7
B 10
C 13
D 16

26. Which statement explains why isotopes of chlorine have the same chemical properties?

A They have the same number of neutrons.
B They have the same nucleon number.
C They have the same electronic configuration.
D They have the same relative atomic mass.

27. The ion X2+ has 20 protons and 18 electrons.

How many electrons are present in one atom of X?

A 18
B 20
C 22
D 40

28. Which electronic configuration is impossible for a neutral atom with proton number less than 20?

A 2,8,8
B 2,8,9
C 2,8,7
D 2,8,8,1

29. Which particle has the same number of protons and electrons?

A Ca2+
B Cl–
C Ar
D O2–

30. An atom has proton number 8 and nucleon number 18.

How many neutrons does it contain?

A 8
B 10
C 18
D 26

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

31. Element X forms X2–. Element Y forms Y+. Both ions have electronic configuration 2,8.

Which statement is correct?

A X has proton number 12 and Y has proton number 9.
B X has proton number 8 and Y has proton number 11.
C X has proton number 10 and Y has proton number 10.
D X has proton number 9 and Y has proton number 12.

32. Which species has 18 electrons and 20 neutrons?

A 40Ca2+
B 39K
C 35Cl–
D 20Ne

33. Which statement about nucleon number is correct?

A It is the number of protons only.
B It is the number of neutrons only.
C It is the total number of protons and neutrons.
D It is the total number of protons and electrons.

34. The particle 27Al3+ is formed from an atom of aluminium.

How many protons, neutrons and electrons does this ion contain?

	protons	neutrons	electrons
A	13	14	10
B	13	27	10
C	14	13	10
D	13	14	16

35. Which atom is in Group VII?

A 2,8,1
B 2,8,2
C 2,8,7
D 2,8,8

36. Which particle has a single positive charge?

A oxide ion
B sulfate ion
C ammonium ion
D carbonate ion

37. An element has isotopes with nucleon numbers 24, 25 and 26.

Which statement must be correct?

A The isotopes have different numbers of protons.
B The isotopes have different numbers of electrons.
C The isotopes have different numbers of neutrons.
D The isotopes have different chemical properties.

38. Which row correctly compares 35Cl and 37Cl?

	protons	neutrons	electrons in neutral atoms
A	same	same	same
B	same	different	same
C	different	same	different
D	different	different	same

39. Which ion has the electronic configuration 2,8,8?

A Al3+
B F–
C Cl–
D Mg2+

40. An atom of element X has 11 protons and 12 neutrons.

Which statement is correct?

A X has nucleon number 11.
B X has nucleon number 23.
C X has 23 electrons.
D X has electronic configuration 2,8,8,1.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

41. Which change produces a negative ion?

A an atom gains electrons
B an atom loses electrons
C an atom gains protons
D an atom loses neutrons

42. The ion Q+ has 18 electrons and 20 neutrons.

What is the nucleon number of Q?

A 18
B 19
C 38
D 39

43. Which pair of particles has the same electronic configuration but different charges?

A Na+ and Mg2+
B Na and Mg
C Cl– and F–
D O2– and S2–

44. Which statement about electrons is correct?

A Electrons are found in the nucleus.
B Electrons have a relative charge of +1.
C Electrons have a much smaller mass than protons.
D Electrons determine the nucleon number.

45. Atom X has electronic configuration 2,8,3. Atom Y has electronic configuration 2,6.

What is the formula of the compound formed between X and Y?

A XY
B X2Y3
C X3Y2
D XY2

46. Which particle has 16 protons and 18 electrons?

A S2–
B S2+
C O2–
D Ar

47. Which statement about relative atomic mass is correct?

A It is always a whole number.
B It depends on the masses and abundances of isotopes.
C It is the same as the nucleon number of the most common isotope only.
D It is the mass of one atom compared with one atom of hydrogen.

48. Element X has relative atomic mass 24.3.

Which statement is most likely?

A All atoms of X have mass 24.3.
B X contains isotopes.
C X contains 24.3 protons.
D X cannot form ions.

49. Which row shows a neutral atom and its most likely ion?

	atom electronic configuration	ion electronic configuration
A	2,8,1	2,8
B	2,8,7	2,8
C	2,8,2	2,8,8
D	2,6	2,4

50. An atom has 17 protons, 18 neutrons and 17 electrons. It gains one electron.

Which statement about the particle formed is correct?

A It has 17 protons, 18 neutrons and 18 electrons.
B It has 18 protons, 18 neutrons and 17 electrons.
C It has 17 protons, 19 neutrons and 18 electrons.
D It has 18 protons, 17 neutrons and 18 electrons.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

1. A

A right: Proton number = protons = 13. Neutrons = 27 – 13 = 14. Neutral atom has 13 electrons.
B wrong: Protons and neutrons are reversed.
C wrong: Neutrons are not equal to nucleon number.
D wrong: Protons are not equal to nucleon number.

2. C

Y2– has 18 electrons, so neutral Y has 16 electrons and 16 protons.
Nucleon number = protons + neutrons = 16 + 16 = 32.

A wrong: 16 is only the number of neutrons/protons.
B wrong: 18 is the number of electrons in the ion.
C right: Nucleon number is 32.
D wrong: 34 adds ion electrons to neutrons, which is not nucleon number.

3. B

A wrong: Na has 11 electrons.
B right: Na+ has lost one electron, so 11 – 1 = 10 electrons.
C wrong: Mg has 12 electrons.
D wrong: F has 9 electrons.

4. B

A wrong: It would not lose one electron because it has 7 outer electrons.
B right: 2,8,7 gains one electron to form a 1– ion with full outer shell.
C wrong: Losing 7 electrons is not likely.
D wrong: Gaining 7 electrons is not likely.

5. A

A right: W and X both have 17 protons but different neutrons, so they are isotopes.
B wrong: W and Y have different proton numbers.
C wrong: X and Z have different proton numbers.
D wrong: Y and Z have different proton numbers.

6. C

A wrong: 2,6 would gain electrons to form 2,8.
B wrong: This is the ion’s configuration, not the neutral atom.
C right: A 2+ ion has lost two electrons, so the neutral atom had 12 electrons: 2,8,2.
D wrong: 2,8,8 has too many electrons.

7. B

A wrong: Period 2 would have only two occupied shells.
B right: Q3+ has 10 electrons, so neutral Q has 13 electrons: 2,8,3. This is Group III, Period 3.
C wrong: Group V elements usually form 3– ions, not 3+.
D wrong: Group V is incorrect.

8. C

A wrong: Nucleon number = 12 + 12 = 24.
B wrong: Atomic number = number of protons = 12.
C right: Proton number 12 means magnesium, which forms Mg2+ by losing two electrons.
D wrong: Magnesium does not usually form 2– ions.

9. B

A wrong: Isotopes have different neutrons, not same neutrons.
B right: Isotopes are atoms of the same element with same protons but different neutrons.
C wrong: Isotopes of the same element have the same proton number but different nucleon numbers.
D wrong: Isotopes have similar chemical properties because their electronic configurations are the same.

10. B

Ar = (75 × 35 + 25 × 37) / 100
Ar = (2625 + 925) / 100
Ar = 35.5

A wrong: Ignores chlorine-37.
B right: 35.5 is correct.
C wrong: Would require equal proportions.
D wrong: Ignores chlorine-35.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

11. C

Let X-65 percentage = y.
63 + 2y/100 = 63.5
2y/100 = 0.5
y = 25%

So X-63 = 75%, X-65 = 25%.

A wrong: This would give a mass closer to 64.5.
B wrong: This would give 64.0.
C right: 75% of X-63 and 25% of X-65 gives 63.5.
D wrong: This would give 63.0.

12. B

A wrong: Cl– has 18 electrons, like argon.
B right: O2– has 10 electrons, same as neon.
C wrong: K+ has 18 electrons.
D wrong: Ca2+ has 18 electrons.

13. C

A wrong: Mg2+ and Al3+ are cations.
B wrong: Na+ is a cation, F– is an anion.
C right: O2– and Cl– are both anions.
D wrong: NH4+ is a cation, SO4 2– is an anion.

14. A

A right: 3 occupied shells means Period 3; 6 outer electrons means Group VI.
B wrong: Group and period are reversed.
C wrong: Period 6 is incorrect.
D wrong: Group III is incorrect.

15. A

Protons = 19, so element is potassium, K.
Nucleon number = 19 + 20 = 39.
Electrons = 18, so charge = +1.

A right: 39K+ is correct.
B wrong: K– would have 20 electrons.
C wrong: Argon has 18 protons, not 19.
D wrong: 20 is not the nucleon number.

16. B

A wrong: –1 charge belongs to electron.
B right: Proton has relative charge +1 and relative mass 1.
C wrong: Neutron has charge 0.
D wrong: 1/1840 is the relative mass of an electron.

17. D

Al3+ = 13 – 3 = 10 electrons
Mg2+ = 12 – 2 = 10 electrons
Na+ = 11 – 1 = 10 electrons
S2– = 16 + 2 = 18 electrons

A wrong: 10 electrons only.
B wrong: 10 electrons only.
C wrong: 10 electrons only.
D right: S2– has 18 electrons.

18. C

A wrong: 2,8,8,1 is Group I, not noble gas.
B wrong: R+ forms by losing, not gaining, one electron.
C right: It loses one outer electron to form R+.
D wrong: Losing an electron gives positive charge, not negative charge.

19. C

A wrong: 2,8,1 has 3 occupied shells.
B wrong: 2,8,8 has 3 occupied shells.
C right: 2,8,8,1 has 4 occupied shells.
D wrong: 2,6 has 2 occupied shells.

20. A

X3– has 10 electrons.
Neutral X has 10 – 3 = 7 electrons, so proton number = 7.

A right: 7 is correct.
B wrong: 10 is the number of electrons in the ion.
C wrong: 13 would form 3+, not 3–.
D wrong: 15 would usually form 3– with 18 electrons.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

21. A

A right: Protons and neutrons are in the nucleus; electrons are in shells.
B wrong: Protons are not in shells.
C wrong: Neutrons are not in shells.
D wrong: Electrons are not in the nucleus.

22. C

A wrong: Positive ions have fewer electrons than protons.
B wrong: Negative ions have more electrons than protons.
C right: Positive ions form when atoms lose electrons.
D wrong: Ions form by electron transfer, not proton transfer.

23. C

Ar = (10 × 20 + 11 × 80) / 100
Ar = (200 + 880) / 100
Ar = 10.8

A wrong: 10.2 would mean isotope 10 is more abundant.
B wrong: 10.5 would mean equal abundance.
C right: 10.8 is correct.
D wrong: 11.0 would mean only isotope 11 exists.

24. A

A right: F– has 10 electrons; Mg2+ has 10 electrons.
B wrong: Na has 11 electrons; Na+ has 10 electrons.
C wrong: Cl– has 18 electrons; F– has 10 electrons.
D wrong: O2– has 10 electrons; Cl– has 18 electrons.

25. C

Ion has 10 electrons after losing 3.
Neutral atom had 10 + 3 = 13 electrons.
So proton number = 13.

A wrong: 7 would form 3–, not 3+.
B wrong: 10 would not lose three electrons to have 10 left.
C right: 13 is correct.
D wrong: 16 would not form this ion.

26. C

A wrong: Chlorine isotopes have different numbers of neutrons.
B wrong: They have different nucleon numbers.
C right: Same electronic configuration gives same chemical properties.
D wrong: Isotopes do not have the same relative atomic mass.

27. B

X2+ has lost two electrons.
If the ion has 18 electrons, neutral X has 20 electrons.

A wrong: 18 is the ion’s electron number.
B right: The atom has 20 electrons.
C wrong: 22 would form X2–, not X2+.
D wrong: 40 is not an electron number here.

28. B

A wrong: 2,8,8 is possible for argon.
B right: 2,8,9 is impossible because the third shell fills to 8 before the fourth shell begins at this level.
C wrong: 2,8,7 is possible for chlorine.
D wrong: 2,8,8,1 is possible for potassium.

29. C

A wrong: Ca2+ has fewer electrons than protons.
B wrong: Cl– has more electrons than protons.
C right: Ar is neutral, so protons = electrons.
D wrong: O2– has more electrons than protons.

30. B

Neutrons = nucleon number – proton number
Neutrons = 18 – 8 = 10

A wrong: 8 is the proton number.
B right: 10 neutrons.
C wrong: 18 is the nucleon number.
D wrong: 26 adds the numbers instead of subtracting.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

31. B

X2– has 10 electrons, so neutral X has 8 electrons/protons.
Y+ has 10 electrons, so neutral Y has 11 electrons/protons.

A wrong: X and Y are reversed incorrectly.
B right: X has proton number 8 and Y has proton number 11.
C wrong: Neutral atoms cannot both have proton number 10 here.
D wrong: Proton numbers are incorrect.

32. A

A right: 40Ca2+ has 20 protons, 20 neutrons and 18 electrons.
B wrong: 39K has 19 electrons, not 18.
C wrong: 35Cl– has 18 electrons but only 18 neutrons.
D wrong: 20Ne has 10 electrons and 10 neutrons.

33. C

A wrong: Proton number is protons only.
B wrong: Neutrons only is not nucleon number.
C right: Nucleon number = protons + neutrons.
D wrong: Electrons are not counted in nucleon number.

34. A

Al has proton number 13.
Neutrons = 27 – 13 = 14.
Al3+ has lost 3 electrons, so electrons = 13 – 3 = 10.

A right: 13 protons, 14 neutrons, 10 electrons.
B wrong: 27 is nucleon number, not neutrons.
C wrong: Protons and neutrons are wrong.
D wrong: Al3+ has fewer electrons, not more.

35. C

A wrong: 2,8,1 is Group I.
B wrong: 2,8,2 is Group II.
C right: 2,8,7 has 7 outer electrons, so Group VII.
D wrong: 2,8,8 is Group VIII/0.

36. C

A wrong: Oxide ion is O2–.
B wrong: Sulfate ion is SO4 2–.
C right: Ammonium ion is NH4+.
D wrong: Carbonate ion is CO3 2–.

37. C

A wrong: Isotopes of the same element have the same protons.
B wrong: Neutral isotopes have the same electrons.
C right: Different nucleon numbers mean different numbers of neutrons.
D wrong: Isotopes usually have the same chemical properties.

38. B

A wrong: Neutrons are not the same.
B right: 35Cl and 37Cl have same protons and electrons, but different neutrons.
C wrong: Proton numbers are the same.
D wrong: Proton numbers are not different.

39. C

A wrong: Al3+ has 10 electrons.
B wrong: F– has 10 electrons.
C right: Cl– has 18 electrons, electronic configuration 2,8,8.
D wrong: Mg2+ has 10 electrons.

40. B

A wrong: Nucleon number is not just protons.
B right: Nucleon number = 11 + 12 = 23.
C wrong: Neutral X has 11 electrons.
D wrong: Proton number 11 gives electronic configuration 2,8,1.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

41. A

A right: Gaining electrons produces a negative ion.
B wrong: Losing electrons produces a positive ion.
C wrong: Atoms do not normally gain protons in chemical reactions.
D wrong: Losing neutrons does not make an ion.

42. D

Q+ has 18 electrons, so neutral Q has 19 protons.
Nucleon number = protons + neutrons = 19 + 20 = 39.

A wrong: 18 is the ion’s electron number.
B wrong: 19 is the proton number.
C wrong: 38 forgets that Q+ has one fewer electron than protons.
D right: 39 is correct.

43. A

A right: Na+ has 10 electrons and Mg2+ has 10 electrons, but charges are different.
B wrong: Na and Mg have different electronic configurations.
C wrong: Cl– has 18 electrons; F– has 10 electrons.
D wrong: O2– has 10 electrons; S2– has 18 electrons.

44. C

A wrong: Electrons are found in shells, not the nucleus.
B wrong: Electrons have relative charge –1.
C right: Electrons have much smaller mass than protons.
D wrong: Nucleon number depends on protons and neutrons.

45. B

X = 2,8,3, so it forms X3+.
Y = 2,6, so it forms Y2–.
Charges balance as X2Y3.

A wrong: XY gives charges +3 and –2, not balanced.
B right: X2Y3 balances 2(+3) with 3(–2).
C wrong: X3Y2 gives +9 and –4.
D wrong: XY2 gives +3 and –4.

46. A

A right: Sulfur has 16 protons. S2– has 16 + 2 = 18 electrons.
B wrong: S2+ has 14 electrons.
C wrong: O2– has 8 protons, not 16.
D wrong: Ar has 18 protons and 18 electrons.

47. B

A wrong: Relative atomic mass is often not a whole number due to isotopes.
B right: It depends on isotope masses and their abundances.
C wrong: It is a weighted average, not just the most common isotope.
D wrong: It is compared with 1/12 of the mass of carbon-12, not hydrogen.

48. B

A wrong: Individual atoms have whole-number isotope masses approximately, not 24.3.
B right: A decimal relative atomic mass suggests a mixture of isotopes.
C wrong: Proton number must be a whole number.
D wrong: Relative atomic mass does not show whether ions form.

49. A

A right: 2,8,1 loses one electron to form 2,8.
B wrong: 2,8,7 gains one electron to form 2,8,8.
C wrong: 2,8,2 loses two electrons to form 2,8.
D wrong: 2,6 gains two electrons to form 2,8.

50. A

A right: Gaining one electron changes only the electron number: 17 protons, 18 neutrons, 18 electrons.
B wrong: Gaining an electron does not change protons.
C wrong: Gaining an electron does not change neutrons.
D wrong: Protons and neutrons do not swap or change.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.