JEE Chemistry Classification of Elements and Periodicity in Properties MCQs Set 23

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Chapter-wise Objective Questions: Classification Of Elements and Periodicity In Properties

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Multiple Choice Questions

Question 1: Which of the following quantities have no unit? (i) electronegativity, (ii) electron gain enthalpy, (iii) ionisation enthalpy, (iv) metallic character
(a) (ii) and (iii) only
(b) (i) and (ii) only
(c) (iii) and (iv) only
(d) (i) and (iv) only
Show Answer & Explanation

Answer: (d) (i) and (iv) only

Explanation:
1. Electronegativity is a relative number on a scale, and metallic character is qualitative.
2. Enthalpies are in kJ/mol.

Teacher's Note:
1. Enthalpy has energy units.
2. Scales are dimensionless.

Question 2: The atomic number of Ag is 47. If the atomic numbers of the elements just above and below Ag in its group are x and y, then (x + y)/12 is
(a) 8
(b) 11
(c) 9
(d) 6
Show Answer & Explanation

Answer: (c) 9

Explanation:
1. x = 29 (Cu) and y = 79 (Au).
2. (29 + 79)/12 = 108/12 = 9.

Teacher's Note:
1. Group 11 members: Cu, Ag, Au.
2. Add the atomic numbers.

Question 3: The most stable oxidation state of thallium is +n. The value of n is
(a) 5
(b) 2
(c) 3
(d) 1
Show Answer & Explanation

Answer: (d) 1

Explanation:
1. Because of the inert pair effect, Tl+ is more stable than Tl3+.

Teacher's Note:
1. The 6s2 pair is inert.
2. Tl(III) is oxidising.

Question 4: How many of the elements Li, Be, C, N, O, F, Ne have a first ionisation energy higher than that of the next element (atomic number + 1)?
(a) 5
(b) 2
(c) 4
(d) 3
Show Answer & Explanation

Answer: (d) 3

Explanation:
1. Be (899) > B (801), N (1402) > O (1314) and Ne (2081) > Na (496).
2. Li < Be, C < N, O < F and F < Ne.

Teacher's Note:
1. Dips in the IE trend occur at group 13 and 16.
2. Ne to Na is a period change.

Question 5: For K(g) + F(g) giving K+(g) + F-(g), the enthalpy change is +18.4 kcal/mol. The ionisation enthalpy of K is 4.3 eV per atom. Taking 1 eV per atom = 23 kcal/mol, if the electron gain enthalpy of F (in eV) is -x/2, the value of x is
(a) 7
(b) 8.6
(c) 3.5
(d) 5
Show Answer & Explanation

Answer: (a) 7

Explanation:
1. 18.4 kcal/mol = 18.4/23 = 0.8 eV.
2. egH of F = 0.8 - 4.3 = -3.5 eV = -7/2 eV, so x = 7.

Teacher's Note:
1. Total enthalpy = IE + egH.
2. Convert kcal to eV.

Question 6: Match the electronic configurations (List I) with the characteristic (List II): P 1s2; Q 1s22s22p5; R 1s22s22p63s23p5; S 1s22s22p2. List II: 1 highest negative oxidation state; 2 highest first ionisation enthalpy; 3 highest electronegativity; 4 maximum electron gain enthalpy. The correct code is
(a) P-1, Q-2, R-3, S-4
(b) P-2, Q-3, R-4, S-1
(c) P-2, Q-1, R-3, S-4
(d) P-4, Q-2, R-3, S-1
Show Answer & Explanation

Answer: (b) P-2, Q-3, R-4, S-1

Explanation:
1. P is helium (highest IE), Q is fluorine (highest EN), R is chlorine (highest egH) and S is carbon (-4, the highest negative state).

Teacher's Note:
1. Identify the elements first.
2. He has the highest IE.

Question 7: Which of the following statements is incorrect?
(a) The first ionisation energy of Na is less than that of Mg
(b) The third ionisation energy of Mg is greater than that of Al
(c) The first ionisation energy of Al is less than that of Mg
(d) The second ionisation energy of Mg is greater than the second ionisation energy of Na
Show Answer & Explanation

Answer: (d) The second ionisation energy of Mg is greater than the second ionisation energy of Na

Explanation:
1. IE2 of Na (4562) is greater than IE2 of Mg (1451) because Na+ has a neon core.
2. The other statements are true (IE3: Mg 7733, Al 2745).

Teacher's Note:
1. Removing core electrons is very hard.
2. Na+ has a noble gas shell.

Question 8: Arrange Li+, Mg2+, K+ and Al3+ in increasing order of size.
(a) K+ < Li+ < Mg2+ < Al3+
(b) Al3+ < Mg2+ < Li+ < K+
(c) Li+ < Mg2+ < Al3+ < K+
(d) Mg2+ < Al3+ < Li+ < K+
Show Answer & Explanation

Answer: (b) Al3+ < Mg2+ < Li+ < K+

Explanation:
1. K+ has an extra shell, so it is the largest.
2. Al3+ and Mg2+ are isoelectronic with Al3+ smaller; Li+ (76 pm) is larger than Mg2+ (72 pm).

Teacher's Note:
1. More shells make it larger.
2. Compare radii: 53, 72, 76, 138 pm.

Question 9: Assertion: The F atom has a less negative electron affinity than the Cl atom. Reason: Additional electrons are repelled more effectively by 3p electrons in Cl than by 2p electrons in F. Which is correct?
(a) Both are true and Reason explains Assertion
(b) Assertion is true but Reason is false
(c) Assertion is false but Reason is true
(d) Both are true but Reason does not explain Assertion
Show Answer & Explanation

Answer: (b) Assertion is true but Reason is false

Explanation:
1. Cl (-349) has a more negative electron affinity than F (-328).
2. The reason is false: the compact 2p electrons of F repel the added electron more than the 3p electrons of Cl.

Teacher's Note:
1. Small size means strong inter-electronic repulsion.
2. The reason is reversed.

Question 10: Which of the following has the correct order of ionic radii?
(a) K+ > Cl-
(b) 35Cl- < 37Cl-
(c) Ti4+ < Mn7+
(d) P3+ > P5+
Show Answer & Explanation

Answer: (d) P3+ > P5+

Explanation:
1. For the same element, the ion with the higher positive charge is smaller, so P3+ > P5+.
2. Mn7+ has a higher charge than Ti4+, isotopes have equal radii, and K+ is smaller than Cl-.

Teacher's Note:
1. Higher positive charge means smaller radius.
2. Isotopes have equal radii.

Question 11: The correct order of radii is
(a) N < Be < B
(b) Fe3+ < Fe2+ < Fe4+
(c) F- < O2- < N3-
(d) Na < Li < K
Show Answer & Explanation

Answer: (c) F- < O2- < N3-

Explanation:
1. F-, O2- and N3- are isoelectronic and the radius increases as nuclear charge decreases.
2. In the other sets, N is smaller than Be and B, Li is smaller than Na and Fe4+ is smaller than Fe2+.

Teacher's Note:
1. Isoelectronic: radius inversely related to Z.
2. Check the others against tables.

Question 12: Assertion: The first ionisation energy of Be is greater than that of B. Reason: The 2p orbital is lower in energy than the 2s orbital. Which is correct?
(a) Assertion is true but Reason is false
(b) Both are true and Reason explains Assertion
(c) Assertion is false but Reason is true
(d) Both are true but Reason does not explain Assertion
Show Answer & Explanation

Answer: (a) Assertion is true but Reason is false

Explanation:
1. Be has a stable filled 2s2 subshell, so IE1 of Be (899) exceeds that of B (801).
2. The 2p orbital is higher in energy than the 2s, so the Reason is false.

Teacher's Note:
1. 2s is lower than 2p for the same shell.
2. B loses its 2p electron more easily.

Question 13: The set that shows the correct order of first ionisation potential is
(a) Be > Mg > Ca
(b) Ge > Si > C
(c) K > Na > Li
(d) B > C > N
Show Answer & Explanation

Answer: (a) Be > Mg > Ca

Explanation:
1. IE falls down a group: Be 899 > Mg 738 > Ca 590.
2. The other sets reverse the trend or ignore the dip at N.

Teacher's Note:
1. Down a group IE decreases.
2. Compare actual values.

Question 14: The least stable ion among Li-, Be-, B- and C- is
(a) Li-
(b) C-
(c) B-
(d) Be-
Show Answer & Explanation

Answer: (d) Be-

Explanation:
1. Be has the filled 2s2 configuration, so the added electron must go into the higher 2p orbital.
2. This makes Be- the least stable.

Teacher's Note:
1. Filled subshells resist extra electrons.
2. Be has a positive egH.

Question 15: Compounds that formally contain Pb4+ are easily reduced to Pb2+. The stability of the lower oxidation state is due to
(a) lanthanoid contraction
(b) diagonal relationship
(c) lattice energy effect
(d) the inert pair effect
Show Answer & Explanation

Answer: (d) the inert pair effect

Explanation:
1. The 6s2 electrons of Pb are held tightly because of poor shielding by 4f and 5d electrons, so Pb(II) is more stable.

Teacher's Note:
1. Heavy p-block elements favour a state two lower than the group number.
2. Pb(IV) is a good oxidant.

Question 16: Among O, Cl, F, N, P, Sn, Tl, Na and Ti, how many elements show only one non-zero oxidation state?
(a) 1
(b) 2
(c) 4
(d) 3
Show Answer & Explanation

Answer: (b) 2

Explanation:
1. Only Na (+1) and F (-1) show a single non-zero state.
2. O, Cl, N, P, Sn, Tl and Ti show more than one.

Teacher's Note:
1. Count elements with one non-zero state.
2. Alkali metals and F.

Question 17: Which series correctly represents the relation between the elements from X to Y?
(a) From F to Br: electron gain enthalpy increases with negative sign
(b) From C to Ge: atomic radii increase
(c) From Ar to Xe: noble character increases
(d) From Li to K: ionisation enthalpy increases
Show Answer & Explanation

Answer: (b) From C to Ge: atomic radii increase

Explanation:
1. Radius increases down a group (C 77 to Ge 122 pm).
2. IE falls from Li to K, the negative egH falls from Cl to Br, and noble character decreases down group 18.

Teacher's Note:
1. Down a group: radius up, IE down.
2. Noble character is reduced down the group.

Question 18: Similarity in the chemical properties of the atoms of elements in a group is most closely related to
(a) the number of valence electrons
(b) atomic numbers
(c) the number of principal energy levels
(d) atomic masses
Show Answer & Explanation

Answer: (a) the number of valence electrons

Explanation:
1. Chemical behaviour is controlled by the valence electrons.

Teacher's Note:
1. Same group means the same outer configuration.
2. Number of shells differs down a group.

Question 19: The increasing order of the ionic radii of O2-, S2-, N3- and P3- is
(a) O2- < N3- < S2- < P3-
(b) O2- < P3- < N3- < S2-
(c) N3- < S2- < O2- < P3-
(d) N3- < O2- < P3- < S2-
Show Answer & Explanation

Answer: (a) O2- < N3- < S2- < P3-

Explanation:
1. Radii (pm): O2- 140, N3- 171, S2- 184, P3- 212.
2. Third period anions are larger than second period ones.

Teacher's Note:
1. Period 3 ions are larger.
2. Within a period, higher charge means larger.

Question 20: In the long form of the periodic table, the valence shell configuration 5s25p4 corresponds to an element in
(a) group 17 and period 5
(b) group 17 and period 6
(c) group 16 and period 5
(d) group 16 and period 6
Show Answer & Explanation

Answer: (c) group 16 and period 5

Explanation:
1. The shell number 5 gives the period and ns2np4 corresponds to group 16.

Teacher's Note:
1. Period = n.
2. Group = 10 + number of s and p electrons.

Question 21: Which of the following statements about periodic properties is true?
(a) All group 17 elements are gases
(b) Group 16 elements have lower ionisation enthalpies than group 15 elements in the corresponding periods
(c) For group 15, the stability of the +5 state increases down the group
(d) All group 13 elements are metals
Show Answer & Explanation

Answer: (b) Group 16 elements have lower ionisation enthalpies than group 15 elements in the corresponding periods

Explanation:
1. The half-filled np3 configuration of group 15 gives higher IE than the np4 of group 16.
2. Boron is a metalloid, Br and I are not gases and the +5 state becomes less stable down group 15.

Teacher's Note:
1. Half-filled configuration is stable.
2. Inert pair effect lowers the highest state.

Question 22: The first three ionisation enthalpies (kJ/mol) of A are 899, 1757, 14847 and of B are 737, 1450, 7731. Which is correct?
(a) Both belong to group 2 and A lies below B
(b) Both A and B belong to group 2 and B lies below A
(c) Both belong to group 1 and A lies below B
(d) Both belong to group 1 and B lies below A
Show Answer & Explanation

Answer: (b) Both A and B belong to group 2 and B lies below A

Explanation:
1. A huge jump occurs after IE2, so both have two valence electrons (group 2).
2. IE1 of B is lower than that of A, so B is below A.

Teacher's Note:
1. Jump identifies the group.
2. Lower IE means a lower position in the group.

Question 23: The electronic configuration with the highest ionisation enthalpy is
(a) [Ne] 3s2 3p3
(b) [Ne] 3s2 3p2
(c) [Ar] 3d10 4s2 4p3
(d) [Ne] 3s2 3p1
Show Answer & Explanation

Answer: (a) [Ne] 3s2 3p3

Explanation:
1. The options are Al, Si, P and As.
2. P has the half-filled 3p3 and is smaller than As, so its IE (1012 kJ/mol) is the highest.

Teacher's Note:
1. IE rises across a period and falls down a group.
2. Half-filled 3p is extra stable.

Question 24: The correct order of increasing ionic radii of Na+, Mg2+, F- and O2- is
(a) Mg2+ < O2- < Na+ < F-
(b) Na+ < Mg2+ < F- < O2-
(c) O2- < F- < Na+ < Mg2+
(d) Mg2+ < Na+ < F- < O2-
Show Answer & Explanation

Answer: (d) Mg2+ < Na+ < F- < O2-

Explanation:
1. These are isoelectronic with 10 electrons; the radius falls as Z increases (8, 9, 11, 12).

Teacher's Note:
1. Isoelectronic: higher Z means smaller.
2. Anions are bigger.

Question 25: When the first electron gain enthalpy of oxygen is -141 kJ/mol, its second electron gain enthalpy is
(a) almost the same as the first
(b) more negative than the first
(c) a positive value
(d) negative but less negative than the first
Show Answer & Explanation

Answer: (c) a positive value

Explanation:
1. The second electron is added to O-, and repulsion makes the process endothermic.

Teacher's Note:
1. Second egH is positive for all elements.
2. Oxides are stable only in a lattice.

Question 26: The effect of lanthanoid contraction in the lanthanoid series is, by and large, a
(a) increase in both atomic and ionic radii
(b) increase in atomic radii and decrease in ionic radii
(c) decrease in atomic radii and increase in ionic radii
(d) decrease in both atomic and ionic radii
Show Answer & Explanation

Answer: (d) decrease in both atomic and ionic radii

Explanation:
1. Poor shielding by 4f electrons raises Zeff, so both atomic and ionic radii decrease across the series.

Teacher's Note:
1. Contraction applies to both.
2. Ln3+ radii also fall from La to Lu.

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