The d-and f-Block Elements VVI Question

 

The d-and f-Block Elements Subjective Question

Q.1. Why do transition elements form coloured compounds ? Explain.

Ans – Transition elements form coloured compounds due to the following reason :

Most of the compounds of transition metals are coloured due to d-d transition, structure defects and charge transfer. Transition metal ions having d0 configuration are colourless.

The explanation is that in the d-d transition, free metal ions has degenerate d-orbital which splits into two levels according to the geometry of complex. Compounds absorb light of visible range for the excitation of electrons from lower to higher level and thus show complementary colour of light is seen.

 

Q.2. Any transition series contains only ten elements. Why ?

Ans – Transition series elements belongs to d-block. Outer most electron in each series of transition metal belongs to d-sub-shell. Also any d-sub-shell can only accomodate maximum number of ten (10) electrons. As one electron is added in each next element, as we proceed in a period, in any transition series.

Therefore, only 10 elements are possible in each series of transition elements.

 

Q.3. Why are Cd2+ salts white ?

Ans – Transition element exhibit colour to d-d transition. d-d transition will be possible only when d-subshell is not fully filled. The electronic configuration of Cd2+ is Cd10 . It means it has fully filled d-subshell. Thus there will be no d-d transition takes place, So Cd2+ is white.

 

Q.4. Why does H3PO3 acts as reducing agent but H3PO4 does not ?

Ans – The reducing nature depends on the number of hydrogen atoms bonded to the central atom. In H3PO3 , It has 1P-H bond whereas in H3PO4 there are no such bonds. Therefore, H3PO3 can release hydrogen and is a better reducing agent. H3PO3 is a better reducing agent than H3PO4.

 

Q.5. Why do transition metals show variable oxidation state ?

Ans – Transition metals show variable oxidation-states due to involvement of ns and (n – 1)d electrons, which have very small energy difference.

 

The d-and f-Block Elements Objective Question

Q.1. The oxidation number of Fe in K4[Fe(CN)6] is – 

(a) +2

(b) +3

(c) -2

(d) -3

Ans – (a) +2

 

Q.2. Transition elements are also known as –

(a) s-block elements

(b) p-block elements

(c) d-block elements

(d) f-block elements

Ans – (c) d-block elements

 

Q.3. Copper sulphate solution on treatment excess of KI gives white precipitate. The precipitate is – 

(a) CuI2

(b) Cu2I2

(c) Cu2SO4

(d) I2

Ans – (a) CuI2

 

Q.4. The highest magnetic moment shown by transition metal ion with the outermost electronic configuration is – 

(a) 3d5

(b) 3d2

(c) 3d7

(d) 3d9

Ans – (a) 3d5

 

Q.5. Oxidation number of gold metal is – 

(a) +1

(b) 0

(c) -1

(d) All of these

Ans – (b) 0

 

Q.6. Which of the following elements is liquid at normal temperature ?

(a) Zinc

(b) Mercury

(c) Bromine

(d) Water

Ans – (b) and (c)

 

Q.7. Which one of the following is dimagnetic ion ?

(a) Co2+

(b) Ni2+

(c) Cu2+

(d) Zn2+

Ans – (d) Zn2+

 

Q.8. Which of the following is not an element of first row of transition series ?

(a) Fe

(b) Cr

(c) Mg

(d) Ni

Ans – (c) Mg

 

Q.9. The transition metal which shows the highest oxidation state is – 

(a) Mn

(b) Pt

(c) Fe

(d) Ni

Ans – (a) Mn

 

Q.10. The cause of variable oxidation state among transition elements is –

(a) They all exist in more than one oxidation state

(b) They all form complex compunds

(c) Valence electrons of them are found in two different sub-shells

(d) They all have paired sub-shells

Ans – (c) Valence electrons of them are found in two different sub-shells.

 

Q.11. An orange solid (A) is – 

(a) Sodium dichromate

(b) Potassium dichromate

(c) Potassium chromate

(d) Ammonium dichromate

Ans – (b) Potassium dichromate

 

Q.12. The green residue (B) has the formula –

(a) CrO2

(b) Cr2O2

(c) Cr2O3

(d) CrO5

Ans – (c) Cr2O3

 

Q.13. The white solid (D) formed is –

(a) NH4Cl

(b) MgO2

(c) NH4OH

(d) (NH4)2CO3

Ans – (b) MgO2

 

Q.14. The cause of variable valency among transition elements is –

(a) They all exist in more than one oxidation states

(b) They all form complex compounds

(c) The valence electrons of them are found in two different sub-shells

(d) They all have paired electrons

Ans – (c) The valence electrons of them are found in two different sub-shells.