d and f Block Elements — Page 6 | JEE Chemistry

Q51

The highest possible oxidation states of uranium and plutonium, respectively are :

A 4 and 6

B 6 and 4

C 7 and 6

D 6 and 7

Correct Answer

Option D

Solution

The highest possible oxidation states of uranium and plutonium can be identified by considering the electronic configurations of these elements and noting the number of valence electrons available for bonding.

Uranium (U, atomic number 92) has the electronic configuration: $[Rn] 5f^3 6d^1 7s^2$ Plutonium (Pu, atomic number 94) has the electronic configuration: $[Rn] 5f^6 7s^2$ To find the highest oxidation state, we sum the number of $d$ , $f$ , and $s$ electrons in the valence shell.

For uranium : $3 (f) + 1 (d) + 2 (s) = 6$ So the highest oxidation state of uranium is +6.

For plutonium : $6 (f) + 2 (s) = 8$ So the highest oxidation state of plutonium is +8.

However, in practice, plutonium is known to exhibit a highest oxidation state of +7.

Comparing with the given options, the correct answer is : Option D : 6 and 7.

Q52

The effect of lanthanoid contraction in the lanthanoid series of elements by and large means :

A increase in atomic radii and decrease in ionic radii

B increase in both atomic and ionic radii

C decrease in both atomic and ionic radii

D decrease in atomic radii and increase in ionic radii

Correct Answer

Option C

Solution

Due to Lanthanoid contraction both atomic radii and ionic radii decreases gradually in the lanthanoid series.

Q53

The transition element that has lowest enthalpy of atomisation, is :

A Fe

B Cu

C V

D Zn

Correct Answer

Option B

Solution

Since Zn is not a transition element so transition element having lowest atomisation energy out of Cu, V, Fe is Cu.

Q54

The element that usually does NOT show variable oxidation states is :

A V

B Cu

C Sc

D ti

Correct Answer

Option C

Solution

Sc3+ has noble gas configuration hence only +3 exists.

Most common oxidation states of : (i) Sc : +3 (ii) V : +2, +3, +4, +5 (iii) Ti : +2, +3, +4 (iv) Cu : +1, +2

Q55

The outer electron configuration of

Gd

(Atomic No.

64

) is :

A

4{f^3}\,5{d^5}\,6{s^2}

B

4{f^8}\,5{d^0}\,6{s^2}

C

4{f^4}\,5{d^4}\,6{s^2}

D

4{f^7}\,5{d^1}\,6{s^2}

Correct Answer

Option D

Solution

The configuration of

Gd

is

4{f^7}\,5{d^1}\,6{s^2}.

Q56

The 71st electron of an element X with an atomic number of 71 enters into the orbital :

A 4f

B 6s

C 6p

D 5d

Correct Answer

Option D

Solution

In lutetium (71Lu) the 71st electron enters in 5d-orbital. Electron configuration is [Xe]4f145d16s2

Q57

The set that contains atomic numbers of only transition elements, is :

A 21, 32, 53, 64

B 9, 17, 34, 38

C 37, 42, 50, 64

D 21, 25, 42, 72

Correct Answer

Option D

Solution

Elements with atomic number 21, 25, 42 and 72 belongs to transition metals.

Tranition elements = 21 to 30 37 to 48 57 & 72 to 80

Q58

Mischmetal is an alloy consisting mainly of :

A lanthanoid and actinoid metals

B actinoid and transition metals

C lanthanoid metals

D actinoid metals

Correct Answer

Option C

Solution

Misch metal is an alloy consisting mainly of lanthanoid metals.

Q59

The lanthanoid that does NOT show +4 oxidation state is :

A Tb

B Dy

C Ce

D Eu

Correct Answer

Option D

Solution

Europium (Eu) Atomic No = 63 Electronic configuration = [Xe]4f76s2 Can show only + 2 and + 3 oxidation state.

Q60

In the sixth period, the orbitals that are filled are :

A 6s, 5d, 5f, 6p

B 6s, 4f, 5d, 6p

C 6s, 6p, 6d, 6f

D 6s, 5f, 6d, 6p

Correct Answer

Option B

Solution

As per (n + l) rule in 6th period, order of orbitals filling is 6s, 4f, 5d, 6p.