The d- and f-Block Elements

Previous Years' CBSE Board Questions

4.2 Electronic Configurations of the d-Block Elements

VSA : (1 mark)

1. Account for the following: Assertion (A): Transition metals have low melting Zn, Cd, Hg are considered as d-block elements but points.

not as transition elements. (1/5, 2020) Reason (R): The involvement of greater number of

OR (n - 1)d and ns electrons in the interatomic metallic

bonding. Account for the following: Zn is not considered as a transition element. (1/5, Al 2014) U

SAI (2 marks)

1. What are the transition elements? Write two characteristics of the transition elements. (Term II, 2021-22C, Delhi 2015)

4.3 General Properties of the Transition Elements (d-Block)

MCQ

Read the given passage and answer the questions

Which property of transition metals enables them to behave as catalysts?

1. High melting point
2. High ionisation enthalpy
3. Alloy formation
4. Variable oxidation states

4 Which of the following is a strong oxidising agent? (At. No. Mn = 25, Zn = 30, Cr = 24, Sc = 21)

1. Mn³⁺ (b) Zn2+ (c) Cr3+ (d) Sc3+

(2021 C)

1. The incorrect statement about interstitial compounds 15
2. they are chemically reactive.
3. they are very hard.
4. they retain metallic conductivity.
5. they have high melting point. (2020) R

1. Out of the following transition elements, the maximum number of oxidation states are shown by
2. Sc (Z = 21) (b) <math>Cr(Z = 24)</math>
3. <math>Mn(Z = 25)</math> (d) Fe <math>(Z = 26)</math>

1. Assertion (A): Transition metals have high melting point. Reason (R): Transition metals have completely filled
2. orbitals.
3. Both Assertion (A) and Reason (R) are correct statements, and Reason (R) is the correct explanation of the Assertion (A).

1. Both Assertion (A) and Reason (R) are correct statements, but Reason (R) is not the correct explanation of the Assertion (A).
2. Assertion (A) is correct, but Reason (R) is incorrect statement.
3. Assertion (A) is incorrect, but Reason (R) is correct statement. (2020)
4. Both Assertion (A) and Reason (R) are correct statements, and Reason (R) is the correct explanation of the Assertion (A).
5. Both Assertion (A) and Reason (R) are correct statements, but Reason (R) is not the correct explanation of the Assertion (A).
6. Assertion (A) is correct, but Reason (R) is incorrect statement.
7. Assertion (A) is incorrect, but Reason (R) is correct statement. (2020)

VSA (1 mark)

number (9 to 13) that follow:

The d-block of the periodic table contains the elements

of groups 3-12 and are known as transition elements. In

general, the electronic configuration of these elements

is <math>(n-1)d^{1-10} ns^{1-2}</math>. The d-orbitals of the penultimate

energy level in their atoms receive electrons giving rise

to three rows of the transition metals i.e., 3d, 4d and 5d

series. However, Zn, Cd and Hg are not regarded as

transition elements. Transition elements exhibit certain

characteristic properties like variable oxidation states,

complex formation, formation of coloured ions and alloys,

catalytic activity, etc. Transition metals are hard (except

Zn, Cd and Hg) and have a high melting point.

1. Why are Zn, Cd and Hg non-transition elements?
2. Which transition metal of 3d series does not show variable oxidation states?

Why do transition metals and their compounds show

catalytic activity?

1. Why are melting points of transition metals high?
2. Why is Cu2+ ion coloured while Zn2+ ion is colourless in aqueous solution? (2020)

Out of zinc and tin, whose coating is better to protect

iron objects? (One word, 2020)

1. Account for the following: Copper(I) compounds are white whereas copper(II) compounds are coloured. (1/5, 2020) Ap
2. Write the formula of an oxoanion of chromium (Cr) in which it shows the oxidation state equal to its group number. (NCERT, Delhi 2017)

1. Write the formula of an oxoanion of manganese (Mn) in which it shows the oxidation state equal to its group number. (Delhi 2017)
2. How would you account for the following: Transition metals form coloured compounds?

(1/3, Delhi 2015) 30. Give reasons:

Zn²⁺ salts are white while Cu²⁺ salts are coloured. Why? (AI 2015) U

Why do transition elements show variable oxidation states? (Delhi 2014C)

SAI (2 marks)

Calculate the spin-only moment of Co2+ (Z = 27) by writing the electronic configuration of Co and Co2+. (2/5, 2020)

Account for the following: (i)

1. Give reason and select one atom/ion which will exhibit asked property:
2. Sc3+ or Cr3+ (exhibit diamagnetic behaviour)
3. Cr or Cu (high melting and boiling point) (2/5, 2020) An

Calculate the number of unpaired electrons in the following gaseous ions: <math>Mn^{3+}</math> and <math>Cr^{3+}</math> (Atomic number of <math>Cr = 24</math>, <math>Mn = 25</math>) Which one of them is most stable in aqueous solution and why? (2020 C)

1. Calculate the number of unpaired electrons in the following gaseous ions: <math>Ti^{3+}</math> and <math>Cr^{3+}</math> (Atomic number of <math>Ti = 22</math>, <math>Cr = 24</math>) Which one of them is most stable in aqueous solution

and why? (2020 C)

Account for the following:

1. Give reasons for the following:
2. Transition metals form alloys.
3. <math>Mn_2O_3</math> is basic whereas <math>Mn_2O_7</math> is acidic. (2/3, Delhi 2019)

1. Use the data to answer the following and also justify giving reasons:

Cr Mn Fe Co EM2+/M -0.91 -1.18 -0.44 -0.28 E°M3+/M2+ -0.41 +1.57 +0.77 +1.97

(2/3, Foreign 2014)

1. Which is a stronger reducing agent in aqueous medium, Cr2+ or Fe2+ and why?
2. Which is the most stable ion in +2 oxidation state and why? (AI 2019)
3. Give reasons:
4. Of the d⁴ species, Cr²⁺ is strongly reducing while Mn³⁺ is strongly oxidising.
5. The <math>d^1</math> configuration is very unstable in ions. (2019 C)

1. (i) How is the variability in oxidation states of transition metals different from that of the
2. block elements?

(ii) Out of Cu⁺ and Cu²⁺, which ion is unstable in

aqueous solution and why? (2/5, Delhi 2017)

Account for the following:

1. (ii) Zn, Cd and Hg are soft metals. (2/5, Al 2017)

(i) Transition metals show variable oxidation states.

(2/3, Delhi 2016) U

Why do transition elements show variable oxidation

states? In 3d series (Sc to Zn), which element shows

the maximum number of oxidation states and why?

(Foreign 2015)

How would you account for the following: (i) Transition metals and their compounds show

catalytic properties. (2/3, Foreign 2015)

What is meant by 'disproportionation'? Give an

example of a disproportionation reaction in aqueous

solution. (NCERT)

(Delhi 2015C, Al 2015C)

1. Mn2+ is more stable than Fe2+ towards oxidation to +3 state.
2. The enthalpy of atomization is lowest for Zn in 3d series of the transition elements. (Delhi 2014)
3. (i) Write two characteristic of the transition elements.

Which of the 3d-block elements may not be

regarded as the transition elements and why?

1. Assign a reason for each of the following observations:
2. The transition metals (with the exception of Zn, Cd and Hg) are hard and have high melting and boiling points.
3. The ionisation enthalpies (first and second) in the first series of the transition elements are found to vary irregularly. (Delhi 2014C)
4. Assign reasons for the following:
5. Copper(I) ion is not known to exist in aqueous solutions.
6. Both O2 and F2 stabilize high oxidation states of transition metals but the ability of oxygen to do so exceeds that of fluorine. (AI 2014C)