1. The incorrect statement among the following is:

• (a) the first ionization enthalpy of Al is less than the first ionization enthalpy of Mg.
• (b) the second ionization enthalpy of Mg is greater than the second ionization enthalpy of Na.
• (c) the first ionization enthalpy of Na is less than the first ionization enthalpy of Mg.
• (d) the third ionization enthalpy of Mg is greater than the third ionization enthalpy of Al.

Correct Answer: (b)

Explanation: The second ionization enthalpy (\( IE_{2} \)) of Mg is actually lower than that of Na. In the case of \( \text{Mg}^{+} \), a \( 3s \)-electron is being removed, whereas in the case of \( \text{Na}^{+} \), an electron must be removed from a stable, inert gas configuration (Neon), which requires significantly more energy.

2. The decreasing order of the ionization potential of the following elements is:

• (a) \( \text{Ne} > \text{Cl} > \text{P} > \text{S} > \text{Al} > \text{Mg} \)
• (b) \( \text{Ne} > \text{Cl} > \text{P} > \text{S} > \text{Mg} > \text{Al} \)
• (c) \( \text{Ne} > \text{Cl} > \text{S} > \text{P} > \text{Mg} > \text{Al} \)
• (d) \( \text{Ne} > \text{Cl} > \text{S} > \text{P} > \text{Al} > \text{Mg} \)

Correct Answer: (b)

Explanation: Higher ionization enthalpies are found in elements with closed shell configurations (Ne), half-filled configurations (P), and completely filled configurations (Mg).

3. In any period, the valency of an element with respect to oxygen:

• (a) increases one by one from IA to VIIA
• (b) decreases one by one from IA to VIIA
• (c) increases one by one from IA to IVA and then decreases from VA to VIIA one by one
• (d) decreases one by one from IA to IVA and then increases from VA to VIIA one by one

Correct Answer: (c)

Explanation: Moving along a period, electrons are added to the outermost shell and valency increases. However, when valence electrons exceed 4, the valency is calculated as \( \text{group number} – 8 \).

4. The electronic configuration of the atom having maximum difference in first and second ionization energies is:

• (a) \( 1s^2 2s^2 2p^6 3s^1 \)
• (b) \( 1s^2 2s^2 2p^6 3s^2 \)
• (c) \( 1s^2 2s^2 2p^1 \)
• (d) \( 1s^2 2s^2 2p^6 3s^2 3p^1 \)

Correct Answer: (a)

Explanation: In configuration (a), the first electron is easily removed from the \( 3s^1 \) orbital. However, the second electron must be removed from a stable Neon core, which is extremely difficult, resulting in the maximum difference between \( IE_1 \) and \( IE_2 \).

5. The electronic configuration and the group number in the periodic table in which the element with atomic number 107 lies are:

• (a) \( [\text{Rn}] 5f^{14} 6d^1 7s^2 7p^4 \), Group 3
• (b) \( [\text{Rn}] 5f^{14} 6d^5 7s^2 \), Group 7
• (c) \( [\text{Rn}] 5f^{14} 7s^2 7p^5 \), Group 7
• (d) \( [\text{Rn}] 5f^{14} 6d^2 7s^2 7p^3 \), Group 15

Correct Answer: (b)

Explanation: Following the Aufbau principle, the electronic configuration for atomic number 107 is \( [\text{Rn}] 5f^{14} 6d^5 7s^2 \), placing it in Group 7.

6. The ionization enthalpy of second period elements vary with atomic number as shown in the provided graph. The elements present at points B and E are:

• (a) Be, C
• (b) B, N
• (c) Be, O
• (d) Be, N

Correct Answer: (d)

Explanation: B corresponds to Beryllium (\( 1s^2 2s^2 \), fully filled) and E corresponds to Nitrogen (\( 1s^2 2s^2 2p^3 \), half-filled). These stable configurations result in higher ionization energies compared to elements in the subsequent groups.

7. As we move from left to right across a period, there is regular decrease in atomic radii of the representative elements. This is due to the reason that:

• (a) the number of energy shells remains the same while nuclear charge decreases
• (b) the number of energy shells remains the same while nuclear charge increases
• (c) the nuclear charge remains the same while number of shells decrease
• (d) both number of shells and nuclear charge remain the same.

Correct Answer: (b)

Explanation: Radius is inversely proportional to nuclear charge. Across a period, the number of shells remains constant while the nuclear charge increases, pulling electrons closer to the nucleus.

8. Which of these solids has the highest density?

• (a) Hg
• (b) Br
• (c) Os
• (d) Ir

Correct Answer: (c)

Explanation: Among the known solids, Osmium (Os) has the highest density.

9. Which of the following is correct?

• (a) van der Waals’ radius of chlorine is bigger than nitrogen.
• (b) Covalent radius of nitrogen is bigger than chlorine.
• (c) van der Waals’ radius of chlorine is smaller than nitrogen.
• (d) All are correct.

Correct Answer: (a)

Explanation: The van der Waals’ radius of chlorine (0.18 nm) is greater than that of nitrogen (0.15 nm).

10. If the resonance energy of C-H bond is \( 24.3 \text{ kJ/mol} \), the electronegativity difference of C and H is:

• (a) 1.02
• (b) 0.50
• (c) 0.80
• (d) 1.04

Correct Answer: (b)

Explanation: Electronegativity difference is calculated as \( 0.101 \sqrt{\Delta_{AB}} \), where \( \Delta_{AB} \) is in kJ/mol. Thus, \( 0.101 \sqrt{24.3} = 0.5 \).

11. Fluorine has the highest electronegativity among the \( ns^2 np^5 \) group on the Pauling scale, but the electron affinity of fluorine is less than that of chlorine because:

• (a) the atomic number of fluorine is less than that of chlorine
• (b) fluorine being the first member of the family behaves in an unusual manner
• (c) chlorine can accommodate an electron better than fluorine by utilising its vacant 3d-orbital
• (d) small size, high electron density and an increased electron repulsion makes addition of an electron to fluorine less favourable than that in the case of chlorine

Correct Answer: (d)

Explanation: The small size and high electron density of fluorine cause increased electron-electron repulsion, making the addition of an electron less favourable than in chlorine.

12. The element of \( 4^{th} \) period of the periodic table having maximum number of unpaired electrons in its ground state is:

• (a) \( {}_{20}\text{Ca} \)
• (b) \( {}_{30}\text{Zn} \)
• (c) \( {}_{33}\text{As} \)
• (d) \( {}_{24}\text{Cr} \)

Correct Answer: (d)

Explanation: Chromium (\( \text{Cr} \)) has the configuration \( 3d^5 4s^1 \), which contains 6 unpaired electrons.

13. The correct arrangement of increasing order of atomic radii among Na, K, Mg, Rb is:

• (a) \( \text{Mg} < \text{K} < \text{Na} < \text{Rb} \)
• (b) \( \text{Mg} < \text{Na} < \text{K} < \text{Rb} \)
• (c) \( \text{Mg} < \text{Na} < \text{Rb} < \text{K} \)
• (d) \( \text{Na} < \text{K} < \text{Rb} < \text{Mg} \)

Correct Answer: (b)

Explanation: Atomic radii decrease across a period and increase down a group. Therefore, the order is \( \text{Mg} < \text{Na} < \text{K} < \text{Rb} \).

14. In which of the following arrangements, the order is not according to the property indicated against it?

• (a) \( \text{Al}^{3+} < \text{Mg}^{2+} < \text{Na}^{+} < \text{F}^{-} \) increasing ionic size
• (b) \( \text{B} < \text{C} < \text{N} < \text{O} \) increasing first ionisation energy
• (c) \( \text{I} < \text{Br} < \text{F} < \text{Cl} \) increasing electron gain enthalpy (without negative sign)
• (d) \( \text{Li} < \text{Na} < \text{K} < \text{Rb} \) increasing metallic radius

Correct Answer: (b)

Explanation: The first ionization enthalpy (\( IE_1 \)) of Nitrogen (\( 1s^2 2s^2 2p^3 \)) is higher than that of Oxygen (\( 1s^2 2s^2 2p^4 \)) because Nitrogen has an extra-stable half-filled \( 2p \)-subshell. The correct order is \( \text{B} < \text{C} < \text{O} < \text{N} \).

15. The correct order of radii is:

• (a) \( \text{N} < \text{Be} < \text{B} \)
• (b) \( \text{F}^{-} < \text{O}^{2-} < \text{N}^{3-} \)
• (c) \( \text{N} < \text{Li} < \text{K} \)
• (d) \( \text{Fe}^{3+} < \text{Fe}^{2+} < \text{Fe}^{4+} \)

Correct Answer: (b)

Explanation: For isoelectronic species, size increases as the magnitude of negative charge increases.

16. An element of atomic number 29 belongs to which of the following block of the periodic table?

• (a) s-block
• (b) p-block
• (c) f-block
• (d) d-block

Correct Answer: (d)

Explanation: The element with \( Z=29 \) has the configuration \( [\text{Ar}]^{18} 3d^{10} 4s^1 \). Since the last electron enters the d-orbital, it is a d-block element.

17. Which one of the following has the largest size?

• (a) Na
• (b) \( \text{Na}^{+} \)
• (c) \( \text{Na}^{-} \)
• (d) None of these

Correct Answer: (c)

Explanation: An anion has a larger size than its parent neutral atom.

18. An element with atomic number 19 will most likely combine chemically with the element whose atomic number is:

• (a) 17
• (b) 18
• (c) 21
• (d) 20

Correct Answer: (a)

Explanation: Ionic bonds form most readily between highly electropositive elements (Alkali metal, \( Z=19 \)) and highly electronegative elements (Halogen, \( Z=17 \)).

19. Lattice energy of an ionic compound depends upon:

• (a) charge on the ion only
• (b) size of the ion only
• (c) packing of the ion only
• (d) charge and size of the ion

Correct Answer: (d)

Explanation: Lattice energy value depends on both the charge and the size of the ion.

20. The increasing order of the first ionisation enthalpies of the elements B, P, S and F (lowest first) is:

• (a) \( \text{F} < \text{S} < \text{P} < \text{B} \)
• (b) \( \text{P} < \text{S} < \text{B} < \text{F} \)
• (c) \( \text{B} < \text{P} < \text{S} < \text{F} \)
• (d) \( \text{B} < \text{S} < \text{P} < \text{F} \)

Correct Answer: (d)

Explanation: Generally, \( IE \) increases across a period and decreases down a group. Phosphorus has a higher \( IE \) than Sulphur due to its stable half-filled configuration (\( 3p^3 \)). Thus, the order is \( \text{B} < \text{S} < \text{P} < \text{F} \).

21. Which of the following does not show variable oxidation number?

• (a) Ba
• (b) N
• (c) V
• (d) Mn

Correct Answer: (a)

Explanation: Barium (Ba) only shows an oxidation number of +2. Nitrogen shows -3 to +5, while V and Mn are transition elements with variable states.

22. The statement that is not true for the long form of the periodic table is:

• (a) it reflects the sequence of filling the electrons in the order of sub-energy levels s, p, d, f
• (b) it helps to predict the stable valence states of the elements
• (c) it reflects trends in physical and chemical properties of the elements
• (d) it helps to predict the relative ionicity of the bond between any two elements.

Correct Answer: (b)

Explanation: The long form of the periodic table does not directly help to predict the stable valence states of elements.

23. Which of the following is not correct for a group in Mendeleev’s periodic table?

• (a) There are nine groups including zero group.
• (b) All the groups are divided into sub groups.
• (c) The group number of element represents its valency.
• (d) The group number of element represents its position in periodic table.

Correct Answer: (b)

Explanation: In Mendeleev’s table, Group VIII is not divided into sub-groups.

24. Which of the following is not correct?

• (a) van der Waals’ radius of fluorine is less than oxygen.
• (b) van der Waals’ radius of nitrogen is more than fluorine.
• (c) van der Waals’ radius of oxygen is less than nitrogen.
• (d) van der Waals’ radius of nitrogen is less than oxygen.

Correct Answer: (d)

Explanation: The van der Waals’ radius of nitrogen (0.15 nm) is greater than that of oxygen (0.14 nm).

25. Which of the following processes involves absorption of energy?

• (a) \( \text{S}_{(g)} + e^{-} \rightarrow \text{S}^{-}_{(g)} \)
• (b) \( \text{O}^{-}_{(g)} + e^{-} \rightarrow \text{O}^{2-}_{(g)} \)
• (c) \( \text{Cl}_{(g)} + e^{-} \rightarrow \text{Cl}^{-}_{(g)} \)
• (d) \( \text{O}_{(g)} + e^{-} \rightarrow \text{O}^{-}_{(g)} \)

Correct Answer: (b)

Explanation: While the first electron affinity (\( EA_1 \)) generally evolves energy, adding a second electron to an already negative ion (\( EA_2 \) of Oxygen) requires energy absorption to overcome electrostatic repulsion.

26. Which of the following does not show amphoteric behaviour?

• (a) \( \text{Zn(OH)}_2 \)
• (b) BeO
• (c) \( \text{Al}_2\text{O}_3 \)
• (d) \( \text{SO}_2 \)

Correct Answer: (d)

Explanation: \( \text{Zn(OH)}_2 \), BeO, and \( \text{Al}_2\text{O}_3 \) are amphoteric. \( \text{SO}_2 \) is acidic.

27. The order of ionization energies of different orbital is:

• (a) \( s > p > d > f \)
• (b) \( p > d > s > f \)
• (c) \( f > d > p > s \)
• (d) \( s = p = d = f \)

Correct Answer: (a)

Explanation: In multi-electron atoms, the probability of finding an electron near the nucleus (penetration effect) follows the order \( s > p > d > f \). S-electrons are held most tightly, leading to higher ionization energies.

28. The second ionization energy is highest for:

• (a) Mg
• (b) Al
• (c) Na
• (d) Si

Correct Answer: (c)

Explanation: After losing one electron, Sodium (\( \text{Na} \)) attains a stable noble gas configuration (\( 1s^2 2s^2 2p^6 \)). Removing a second electron requires a very high amount of energy.

29. Which of the following is correct?

• (a) Ionization energy of noble gasses is highest in respective periods.
• (b) Ionization energy of group-1 metals is lowest in respective periods.
• (c) Ionization energy of Al and Ga is almost same.
• (d) All are correct.

Correct Answer: (d)

Explanation: Noble gases have stable configurations; Group 1 metals are the largest in their periods (easiest to remove electrons); and the sizes of Al and Ga are nearly identical due to the poor shielding by d-electrons in Ga.

30. Which of the following statements is not correct about modified Mendeleev’s periodic table?

• (a) It consists of nine groups and seven periods.
• (b) Group VIII like group I-VIII has been divided into two sub-groups A and B.
• (c) The group of an element in the periodic table represents its valency.
• (d) The elements of group IB are called coinage metals.

Correct Answer: (b)

Explanation: In the modified Mendeleev table, Group VIII consists of three triads (e.g., Fe, Co, Ni) and is not divided into A and B sub-groups.

31. The element cited as an example to prove the validity of Mendeleev’s periodic law is:

• (a) germanium
• (b) scandium
• (c) gallium
• (d) all of these

Correct Answer: (d)

Explanation: Mendeleev left blank spaces and predicted the properties of elements like Scandium, Gallium, and Germanium before their actual discovery.

32. The number of elements known at that time when Mendeleev arranged them in the periodic table was:

• (a) 63
• (b) 60
• (c) 71
• (d) 65

Correct Answer: (a)

Explanation: Only 63 elements were known when Mendeleev first framed his periodic table.

33. The effective nuclear charge of \( \text{Mg} (Z=12) \) is:

• (a) 3
• (b) 2
• (c) 4
• (d) 1

Correct Answer: (a)

Explanation: Calculating with Slater’s rules, the shielding constant \( \sigma \approx 9.15 \). \( Z^{*} = 12 – 9.15 = 2.85 \approx 3 \).

34. Ionization potential and electron affinity of fluorine are 17.42 and 3.45 eV atom\( ^{-1} \) respectively. Electronegativity of fluorine will be approximately:

• (a) 3
• (b) 6
• (c) 4
• (d) 2

Correct Answer: (c)

Explanation: Electronegativity can be calculated as \( 0.374 \frac{[IE + EA]}{2} + 0.17 \). For Fluorine: \( 0.374 \frac{[17.42 + 3.45]}{2} + 0.17 = 4.07 \approx 4 \).

35. The energy required to convert all the atoms of magnesium to magnesium ions present in 24 mg of magnesium vapours is: (First and second ionization enthalpies of Mg are 737.76 and 1450.73 kJ mol\( ^{-1} \) respectively).

• (a) 2 kJ
• (b) 102 kJ
• (c) 92 kJ
• (d) 112 kJ

Correct Answer: (a)

Explanation: Total energy per mole = \( 737.76 + 1450.73 = 2188.49 \text{ kJ/mol} \). Since 24 mg is \( 10^{-3} \text{ mole} \), the energy required is \( 2188.49 \times 10^{-3} \approx 2 \text{ kJ} \).

36. The correct decreasing order of first ionisation enthalpies of five elements of the second period is:

• (a) \( \text{Be} > \text{B} > \text{C} > \text{N} > \text{F} \)
• (b) \( \text{N} > \text{F} > \text{C} > \text{B} > \text{Be} \)
• (c) \( \text{F} > \text{N} > \text{C} > \text{Be} > \text{B} \)
• (d) \( \text{N} > \text{F} > \text{B} > \text{C} > \text{Be} \)

Correct Answer: (c)

Explanation: Across the period, \( IE \) increases as nuclear charge increases and size decreases (\( \text{F} > \text{N} > \text{C} \)). However, \( IE \) of Be is higher than B because Be’s electron is removed from a stable \( 2s \)-orbital, whereas B’s is from a \( 2p \)-orbital.

37. The lightest metal in the periodic table is:

• (a) H
• (b) Mg
• (c) Ca
• (d) Li

Correct Answer: (d)

Explanation: Lithium (Li) is the lightest metal in the periodic table.

38. The statement that is not correct for the periodic classification of elements is:

• (a) the properties of elements are the periodic functions of their atomic number
• (b) non-metallic elements are lesser in number than metallic elements
• (c) the first ionization energies of elements along a period do not vary in a regular manner with increase in atomic number
• (d) for transition elements the d-subshells are filled with electrons monotonically with increase in atomic number

Correct Answer: (d)

Explanation: The filling of d-subshells is not monotonic due to exceptions like Chromium (\( 3d^5 4s^1 \)) and Copper (\( 3d^{10} 4s^1 \)).

39. Modern periodic table is based on the atomic number of the elements. The experiment which proved the significance of the atomic number was:

• (a) Millikan’s oil drop experiment
• (b) Moseley’s work on X-ray spectra
• (c) Bragg’s work on X-ray diffraction
• (d) discovery of X-rays by Roentgen

Correct Answer: (b)

Explanation: Moseley’s work on X-ray spectra provided the scientific basis for the modern periodic law, showing that properties are functions of atomic number.

40. Which of these statements gives the correct picture regarding the periodic trends of chemical reactivity?

• (a) The reactivity decreases in the alkali metals but increases in the halogens with increase in atomic number down the group.
• (b) In both the alkali metals and the halogens the chemical reactivity decreases with increase in atomic number down the group.
• (c) Chemical reactivity increases with increase in atomic number down the group in both the alkali metals and halogens.
• (d) In alkali metals the reactivity increases but in the halogens it decreases with increase in atomic number down the group.

Correct Answer: (d)

Explanation: For metals, reactivity increases down the group as ionization energy decreases. For non-metals, reactivity decreases down the group as electron affinity decreases.

41. The electronic configuration of four elements are: (i) [Xe] \( 6s^2 \); (ii) [Xe] \( 4f^{14} 5d^1 6s^2 \); (iii) [Ar] \( 4s^2 4p^5 \); (iv) [Ar] \( 3d^7 4s^2 \). Which statement is not true?

• (a) (i) is a strong reducing agent.
• (b) (ii) is a d-block element.
• (c) (iii) has high negative electron gain enthalpy.
• (d) (iv) shows variable oxidation states.

Correct Answer: (b)

Explanation: Element (ii) is the last member of the Lanthanide series, making it an f-block (specifically, 4f) element, not a d-block element.

42. \( \text{Na}^{+}, \text{Mg}^{2+}, \text{Al}^{3+} \text{ and } \text{Si}^{4+} \) are isoelectronic ions. Their ionic size follows the order:

• (a) \( \text{Na}^{+} < \text{Mg}^{2+} < \text{Al}^{3+} < \text{Si}^{4+} \)
• (b) \( \text{Na}^{+} < \text{Mg}^{2+} < \text{Al}^{3+} > \text{Si}^{4+} \)
• (c) \( \text{Na}^{+} < \text{Mg}^{2+} > \text{Al}^{3+} > \text{Si}^{4+} \)
• (d) \( \text{Na}^{+} > \text{Mg}^{2+} > \text{Al}^{3+} > \text{Si}^{4+} \)

Correct Answer: (d)

Explanation: As the \( Z/e \) ratio increases (nuclear charge per electron), the attraction increases and ionic size decreases.

43. What would be the atomic number of the next halogen if discovered in future?

• (a) 115
• (b) 119
• (c) 117
• (d) 121

Correct Answer: (c)

Explanation: The next halogen will follow the filling of \( 5f \)- and \( 6d \)-orbitals (completing at atomic number 112) plus 5 additional electrons in the \( 7p \)-orbital, resulting in atomic number 117.

44. Identify the correct order of decreasing bond strength in the bonds formed by 2s-2s, 2p-2p, and 2s-2p overlapping.

• (a) \( 2s-2s > 2s-2p > 2p-2p \)
• (b) \( 2s-2s > 2p-2p > 2s-2p \)
• (c) \( 2p-2p > 2s-2p > 2s-2s \)
• (d) \( 2p-2p > 2s-2s > 2s-2p \)

Correct Answer: (c)

Explanation: Bond strength is determined by the extent of overlapping. Maximum overlapping occurs between p-orbitals.

45. The lowest first ionization enthalpy would be associated with which of the following structures?

• (a) \( 1s^2 2s^2 2p^6 3s^1 \)
• (b) \( 1s^2 2s^2 2p^5 \)
• (c) \( 1s^2 2s^2 2p^6 \)
• (d) \( 1s^2 2s^2 2p^6 3s^2 3p^2 \)

Correct Answer: (a)

Explanation: Structure (a) represents Sodium, which has only one electron in its outermost \( 3s \)-subshell, making it very easy to remove.