This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “D and F-Block Elements – Lanthanoids”.
1. The lanthanides are d-block elements.
Explanation: The lanthanides are elements in which the differentiating electron enters (n-2)f-orbital of anti-penultimate shell and are called as f-block elements. These have three outer shells incomplete. Thus, lanthanides are f-block elements, not d-block.
2. What is the general electronic configuration of the lanthanides?
a) (n-2)f 1-14 (n-1)d 1-10 ns2
b) (n-2)f 1-14 (n-1)d 1-2 ns2
c) (n-2)f 1-14 (n-1)d 0-1 ns2
d) (n-2)f 1-14 (n-1)d 0 ns2
Explanation: In lanthanides, the differentiating electron occupies 4f subshell and are rarely found on the earth’s crust, so called rare earths. The general electronic configuration of lanthanides is 6s25d0-14f1-14.
3. What happens to the atomic size of the lanthanides with increase in atomic number?
a) The radius remains unchanged
b) The radius decreases
c) The radius increases
d) The radius first increases and then decreases
Explanation: The gradual decrease in the atomic and ionic radii of the lanthanides with an increase in atomic number is called lanthanide contraction. It occurs due to the poor shielding effect of the 4f electrons.
4. Which of the following is not a consequence of lanthanide contraction?
a) From La+3 to Lu+3, the ionic radii changes from 106 pm to 85 pm
b) As the size of the lanthanide ions decreases the basic strength increases
c) The basic character of oxides and hydroxides decreases with increase in atomic number
d) The atomic radii of 4d and 5d series is similar
Explanation: The small average decreases in the atomic size is responsible for a small decrease in electronegativity and S.O.P of lanthanides. As the size of the lanthanide ions decreases the covalent character of M—OH bond increases and hence basic strength decreases.
5. What is the most common oxidation state of lanthanides?
Explanation: The most common and stable oxidation state of lanthanides is +3. Some elements also exhibit +4 oxidation states. Some elements exhibit +2 oxidation state also due to their half-filled, fully-filled and noble gas configuration.
6. In lanthanides, Ce changes from +4 to +3 oxidation state.
Explanation: In lanthanides, Ce changes from +4 to +3 oxidation state. Formation of Ce4+ is favorable due to its noble gas configuration. However, Ce+4 changes to Ce+3 as it is a strong oxidizing agent. The E° value of Ce+4/Ce+3 is +1.74 V.
7. Which of the following is not a property of lanthanides?
a) They are soft metals with white silvery color
b) They tarnish rapidly by air
c) The hardness of the metals increases with increase in the atomic number
d) The melting point of the metal ranges from 500-1000K
Explanation: All lanthanides are soft metals with silvery white color. They tarnish rapidly by air. With increase in atomic number, the harness of these metals also increases. The melting points of the lanthanides ranges from 1000 to 1200K but samarium melts at 1623K.
8. Which of the following lanthanide ions do not exhibit color?
a) Lu+3 and Ln+3
b) Lu+2 and Ln+2
c) Ce+3 and Ce+3
d) Pr+4 and Ce+4
Explanation: Many trivalent lanthanide ions are colored both in the solid state and in aqueous state due to f-f electronic transition. Lu+3 and Ln+3 don’t exhibit color due to absence of unpaired electrons. All lanthanide ions except La+3, Ce+3 and Lu+3 are paramagnetic due to presence of unpaired electrons.
9. Which of the following is the correct order of arrangement of the first five lanthanides according to atomic number?
a) La, Ce, Pr, Nd, Pm
b) La, Pr, Ce, Pm, Nd
c) La, Pr, Ce, Nd, Pm
d) La, Ce, Pr, Pm, Nd
Explanation: The first five elements of Lanthanides are:
Lanthanum (La) – 57
Cerium (Ce) – 58
Praseodymium (Pr) – 59
Neodymium (Nd) – 60
Promethium (Pm) – 61.
10. Which is the last element of lanthanides?
Explanation: The atomic numbers of Erbium, Thulium, Ytterbium and Lutetium is 68, 69, 70 and 71 respectfully. So the last element of lanthanide series is Lutetium with electronic configuration [Xe]4f145d16s2.
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