Which of the following is not an actinide ?

Curium
Californium
Uranium
Terbium

Solution

Terbium is lanthanide as it belongs to 4f– series having configuration [Xe]4s⁹6s². However the remaining members belong to 5f– series (actinides).

The approximate percentage of iron in mischmetal is

Solution

Mischmetal is an alloy which contains rare earth elements (94-95%), iron (5%) and traces of sulphur,carbon, silicon, calcium and aluminium. It is used in gas lighters, tracer bullets and shells.

Lanthanum is grouped with f-block elements because

it has partially filled f-orbitals
it is just before Ce in the periodic table
it has both partially filled f and d-orbitals
properties of lanthanum are very similar to the elements of f-block

The Ce (Z = 58) belongs to III rd group of periodic table.If it furnish one α particle to form an element ‘X’, then X belongs to

III^rd group
II^nd group
I^st group
zero group

Solution

₅₈Ce is lanthanide. Lanthanides are from 57 to 71 all present in III^rd group. Hence ₅₈Ce forms ₅₆X element on emission of one α particle with belongs to II^nd group.

The titanium (atomic number 22) compound that does not exist is

TiO
TiO₂
K₂TiF₆
K₂TiO₄

Solution

Oxidation state of Ti in the given compounds.as follows:

TiO – + 2

TiO₂ – + 4

TiCl₃ – + 3

K₂TiF₆ – + 4

K₂TiO₄ – + 6

The oxidation states exhibited by Ti is + 2, +3, + 4. So K₂TiO₄ does not exist.

For making Ag from AgNO₃, which of the following is used

PH₃
phosphonium iodide
Na₂CO₃
NH₃

Solution

When AgNO₃ reacts with 3PH, then Ag is obtained.

\(\underset{silver\, nitrate}{6AgNO_{3}}+ \underset{phosphene} {2PH_{3}}\rightarrow 6Ag + \underset{phosphorous\, acid}{2H_{3}PO_{3}}+6NO_{2}\)

Which of the following factors may be regarded as the main cause of lanthanoide contraction?

Greater shielding of 5d electrons by 4 felectrons
Poorer shielding of 5d electrons by 4 felectrons
Effective shielding of one of 4 felectrons by another in the subshell
Poor shielding of one of 4 felectron by another in the subshell

Solution

In lanthanides, there is poorer shielding of 5d electrons by 4 felectrons resulting in greater attraction of the nucleus over 5d electrons and contraction of the atomic radii.

Which of the following compounds is formed when a mixture of K₂Cr₂O₇ and NaCl is heated with conc. H₂SO₄ ?

CrO₂Cl₂
CrCl₃
Cr₂(SO₄)₃
Na₂CrO₄

Solution

K₂Cr₂O₇ + 4KCl + 6H₂SO₄ \(\overset{Heat}{\rightarrow}\) 2CrO₂Cl₂ + 6KHSO₄ + 3H₂O

The radius of La³⁺(Atomic number of La = 57) is 1.06 Å.Which one of the following given values will be closest to the radius of Lu³⁺(Atomic number of Lu= 71) ?

1.40 Å
1.06 Å
0.85 Å
1.60 Å

Solution

Aufbau principle does not give the correct arrangement of filling up of atomic orbitals in:

Cu and Zn
Co and Zn
Mn and Cr
Cu and Cr

Solution

Electronic configuration of Cr is [Ar] 3d⁵4s¹ because this gives it a stable half filled d⁵ configuration. Similarly,electronic configuration of Cu is [Ar]3d¹⁰4s¹. This filling of electrons is not in accordance with Aufbau principle.

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