Online Test: The d- and f-Block Elements | Class 12 Chemistry

Question 1 of 20

The general outer electronic configuration of d-block elements is:

$(n-1)d^{1-10}\,ns^{0-2}$

$ns^{1-2}\,np^{1-6}$

$(n-2)f^{1-14}$

$ns^2\,np^6$

Explanation: d-block elements progressively fill the $(n-1)d$ subshell with $ns$ electrons in the outermost shell.

Question 2 of 20

The configuration of chromium (Z = 24) is:

$[\text{Ar}]3d^4\,4s^2$

$[\text{Ar}]3d^5\,4s^1$

$[\text{Ar}]3d^6$

$[\text{Ar}]3d^3\,4s^2$

Explanation: A $4s$ electron shifts to $3d$ to give the stable half-filled $3d^5$ configuration.

Question 3 of 20

Which of the following is NOT a typical transition element?

Fe

Cr

Mn

Zn

Explanation: Zn is $d^{10}$ in atom and ion, so it shows no characteristic transition-metal properties.

Question 4 of 20

The element with the maximum number of oxidation states in the 3d series is:

Sc

Ti

Mn

Cu

Explanation: Manganese ($3d^5\,4s^2$) exhibits +2 to +7.

Question 5 of 20

The spin-only magnetic moment of $\text{Mn}^{2+}$ ($3d^5$) is:

1.73 BM

2.84 BM

4.90 BM

5.92 BM

Explanation: $n=5$, so $\mu=\sqrt{5\times7}=\sqrt{35}=5.92$ BM.

Question 6 of 20

Colour of transition-metal compounds is mainly due to:

nuclear transitions

d-d electronic transitions

isotope effects

s-p transitions

Explanation: Electrons move between split d orbitals, absorbing visible light.

Question 7 of 20

Which ion is colourless?

$\text{Cu}^{2+}$

$\text{Ti}^{3+}$

$\text{Sc}^{3+}$

$\text{Co}^{2+}$

Explanation: $\text{Sc}^{3+}$ is $3d^0$, so no d-d transition can occur.

Question 8 of 20

In acidic medium permanganate ion is reduced to:

$\text{MnO}_2$

$\text{Mn}^{2+}$

$\text{MnO}_4^{2-}$

Mn metal

Explanation: $\text{MnO}_4^-+8\text{H}^++5e^-\rightarrow\text{Mn}^{2+}+4\text{H}_2\text{O}$.

Question 9 of 20

The oxidation state of chromium in $\text{K}_2\text{Cr}_2\text{O}_7$ is:

+3

+6

+7

+2

Explanation: Each Cr is +6 in the dichromate ion.

Question 10 of 20

On making a dichromate solution alkaline it turns:

orange

green

yellow

colourless

Explanation: Base converts orange dichromate to yellow chromate ($\text{CrO}_4^{2-}$).

Question 11 of 20

The catalyst used in the Contact process is:

Fe

Ni

$\text{V}_2\text{O}_5$

Pt-Rh

Explanation: $\text{V}_2\text{O}_5$ catalyses the oxidation of $\text{SO}_2$ to $\text{SO}_3$.

Question 12 of 20

Steel is an example of a/an:

intermetallic compound

interstitial compound

ionic compound

molecular solid

Explanation: Carbon atoms occupy interstitial holes in the iron lattice.

Question 13 of 20

The lanthanoids are characterised by the filling of:

$3d$ orbitals

$4f$ orbitals

$5f$ orbitals

$6d$ orbitals

Explanation: The $4f$ subshell is progressively filled across the lanthanoid series.

Question 14 of 20

The most stable oxidation state of the lanthanoids is:

+2

+3

+4

+6

Explanation: +3 is the characteristic and most stable state.

Question 15 of 20

Lanthanoid contraction arises because $4f$ electrons:

shield very well

shield poorly

are removed

expand the atom

Explanation: Poor shielding by diffuse $4f$ orbitals raises the effective nuclear charge.

Question 16 of 20

A consequence of lanthanoid contraction is that:

Na and K differ greatly

Zr and Hf have nearly equal radii

all metals become gases

d orbitals disappear

Explanation: Hf is contracted so its radius is almost equal to Zr, making separation hard.

Question 17 of 20

All actinoid elements are:

colourless

radioactive

diamagnetic

s-block elements

Explanation: Every actinoid is radioactive.

Question 18 of 20

The spin-only magnetic moment of $\text{Ti}^{3+}$ ($3d^1$) is:

0 BM

1.73 BM

2.84 BM

3.87 BM

Explanation: $n=1$, $\mu=\sqrt{1(1+2)}=\sqrt{3}=1.73$ BM.

Question 19 of 20

Why is mercury a liquid at room temperature?

It has many unpaired d electrons

Filled $d^{10}$ subshell gives weak metallic bonding

It is a non-metal

It has very high melting point

Explanation: No unpaired d electrons means weak metallic bonding.

Question 20 of 20

Which is the correct half-reaction of dichromate in acid?

$\text{Cr}_2\text{O}_7^{2-}+14\text{H}^++6e^-\rightarrow2\text{Cr}^{3+}+7\text{H}_2\text{O}$

$\text{Cr}_2\text{O}_7^{2-}+2e^-\rightarrow2\text{CrO}_4^{2-}$

$\text{Cr}^{3+}+3e^-\rightarrow\text{Cr}$

$\text{Cr}_2\text{O}_7^{2-}\rightarrow2\text{Cr}^{6+}$

Explanation: Dichromate gains 6 electrons in acid to give two $\text{Cr}^{3+}$ ions.

Online Test — The d- and f-Block Elements