CBSE Class 12 Chemistry Chapter 8 Important Questions – Free PDF Download
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Important Questions Class 12 Chemistry Chapter 8 – The d and f Block Elements
CBSE Class 12 Chemistry Important Questions Chapter 8 – The d and f Block Elements
3 Marks Questions
1. Transition metals generally form coloured ions. Why? Which of the following will be colored? 
Ans. Transition metals form coloured ions due to d-d transition. Coloured ions will be those which have unpaired electrons.
 |  | Colourless |
 |  | Coloured |
 |  | Coloured |
 |  | Colourless |
 |  | Coloured. |
2. Explain the steps of preparation of potassium dichromate?
Ans. Preparation of potassium dichromate takes place in three steps.
Step 1: Fusion of chromite ore with sodium or potassium carbonate in free excess of air.
Step 2: Conversion of Sodium Chromate to Sodium Dichromate by acidifying it.
Step 3: Conversion of sodium dichromate to potassium dichromate by reaching it with KCl.
3. What is the lanthanoid contraction? What are its causes and consequences?
Ans. Lanthanoid contractions – The cumulative effect of the regular decrease in size or radii of Lanthanoid with increase in atomic number is called Lanthanoid contraction.
Causes – The shape of f orbitals is diffused. They have poor shielding effect due to which the effective nuclear charge increase with increase in atomic number. This causes a decrease in atomic radii
Consequences – Due to Lanthanoid contraction-
1. Radii of the members of the third transition series is similar to those of second transition series.
2. It becomes difficult to separate Lanthanoids.