D And F Block Elements(12th Grade > Chemistry ) Questions and answers for exam Preparation

Question 1. The correct order of

E^{0} M^{2 +} / M

values with negative sign for the four successive elements Cr, Mn, Fe and Co is

Fe>Mn>Cr>Co
Cr>Mn>Fe>Co
Mn>Cr>Fe>Co
Cr>Fe>Mn>Co.

Explanation:-

Answer: Option C. -> Mn>Cr>Fe>Co
:
C

E^{0}

values of

M^{2 +} / M

with negative sign are: Cr=-0.91V, Mn= -1.18V, Fe=-0.44V,Co= -0.28V. Thus, the order is Mn

>

Cr

>

Fe

>

Co.

Question 2. The correct order of ionic radii for

Y^{3 +}, E u^{3 +}, L a^{3 +}, L u^{3 +}

La3+
Y3+
Lu3+
Lu3+

Explanation:-

Answer: Option B. -> Y3+
:
B
Y belongs to

5^{t h}

period & La belongs to

6^{t h}

period. Ionic radii increases from

Y^{3 +} t o L a^{3 +}

down the group. Due to lanthanoid contraction, ionic radii follows the order

L u^{3 +} < E u^{3 +} < L a^{3 +}

Question 3. Read the assertion and reason carefully to mark the correct option out of the options given below:
(a)If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b)If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c)If assertion is true but reason is false.
(d)If assertion is false but reason is true.
Assertion: Ionisation enthalpies for early actinoids are lower than that for early lanthanoids.
Reason: 5f electrons more effectively shielded from the nuclear charge than the 4f electrons
of the corresponding lanthanoids.

a
b
c
d

Explanation:-

Answer: Option A. -> a
:
A
Although the 5forbitals resemble the 4forbitals in their angular part of the wave-function, they are not as buried as 4forbitals and hence 5felectrons are less firmly heldin actinoids.

Question 4. Among the following, the compound that is both paramagnetic and coloured is

K2Cr2O7
(NH4)2(TiCl6)
VOSO4
K3[Cu(CN4)]

Explanation:-

Answer: Option C. -> VOSO4
:
C

V^{+ 4} \to 3 d^{1} 4 s^{0}

1 unpaired electrons. Hence, it is paramagnetic and coloured compound.

Question 5. Choose incorrect option:-

MnO2 for use in dry battery cells.
TiCl4 with Al(CH3)3 forms the basis of the Ziegler catalysts used to manufacture polyethylene.
In the Wacker process the oxidation of ethyne to ethanal is catalysed by Hg2Cl2.
Nickel complexes are useful in the polymerisation of alkynes and other organic compounds such as benzene.

Explanation:-

Answer: Option C. -> In the Wacker process the oxidation of ethyne to ethanal is catalysed by Hg2Cl2.
:
C
- In the Wacker process the oxidation of ethyne to ethanal is catalysed by

P d C l_{2}

Question 6. Atomic number of Cr and Fe are 24 and 26 respectively. Which of the following is paramagnetic with the spin of electron?

[Cr(NH3)6]+3
[Fe(CO)5]
[Fe(CN)6]−4
[Cr(CO)6]

Explanation:-

Answer: Option A. -> [Cr(NH3)6]+3
:
A
All metal carbonyls are diamagnetic cyanide complexes are also diamagnetic. Cyanide ion and Carbonyls are strong field ligands causing d-orbital electrons of metal ion to pair up.

Question 7. Which of the following pairs involves isoelectronic ions?

Mn3+ and Fe2+
Mn2+ and Fe3+
Cr3+ and mn2+
Fe2+ and CO2+

Explanation:-

Answer: Option B. -> Mn2+ and Fe3+
:
B
Mn

^{2 +}

and Fe

^{3 +}

ions have 23 electrons, thus, they are isoelectronic.

Question 8. Identify the correct pair of colorless species-

CoF3−6 and NiCl2−4
TiF2−6 and CoF3−6
TiF2−6 and Cu2Cl2
Cu2Cl2 and NiCl2−4

Explanation:-

Answer: Option C. -> TiF2−6 and Cu2Cl2
:
C

\begin{matrix} C o - o r d i n a t i o n c o m p l e x & M e t a l i o n & U n p a i r e d e l e c t r o n s i n m e t a l i o n & N a t u r e o f c o m p l e x C o F_{6}^{3 -} & C o^{3 -} & 4 & P a r a m a g n e t i c N i C l_{4}^{2 -} & N i^{2 +} & 2 & P a r a m a g n e t i c T i F_{6}^{2 -} & T i^{4 +} & 0 & D i a m a g n e t i c C u_{2} C l_{2} & C u^{+} & 0 & D i a m a g n e t i c \end{matrix}

Question 9. The reason for the stability of Gd

^{3} +

ion is

4 f sub shell empty
4 f sub shell- completely filled
Possesses the general electronic configuration of noble gases
4 f sub shell- half filled

Explanation:-

Answer: Option D. -> 4 f sub shell- half filled
:
D
Gd=

4 f^{7} 5 d^{1} 6 s^{2}; G d^{3 +} = 4 f^{7}

Question 10. The colour of light absorbed by an aqueous solution of

C u S O_{4}

is:

orange-red
blue-green
yellow
violet

Explanation:-

Answer: Option A. -> orange-red
:
A
The aqueous blue solution of

C u S O_{4}

absorbs orange-red colour of light