Question

10. Which is colourless in water ?
1) Ti3+
3) Co2+
4) Sc3+
2) V3+​

Answer 1

Answer:

Sc³⁺ is colourless in water.

Explanation:

This is completely a question of d-d transition.

A d-d transition means the shifting of electrons between the lower energy d orbital to a higher

energy d orbital by absorption of energy and vice versa.

In complex compounds the e. g an octahedral complex the electronic transition occurs from a t₂g

orbital to an Eg orbital And generally this transition involves energy in the visible region and thus

Colors are observed. So generally complex compounds are coloured due to transition between the

lower energy d orbital (t₂g orbitals: dxy, dyz and dzx) and higher energy d orbital (Eg orbitals:

dx²,dy² and dz²).

These all are completely D block elements and in the D Block Elements the colour comes due to

completely d- d transition , the compounds which do not show d- d transition do not have any kind

of colour for example d₀ and d ₁₀ configuration and the compounds which have d- d transitions

show the colour all the compounds from d₁ to d₉ configuration have transition

Ti³⁺ = [ Ar ] 3d¹

Here we can see that there is presence of 1 electron in d orbital which will cause d- d transition

and hence further causes colour.

Co²⁺ =[Ar ] 3d⁷

Here we can see that there is presence of 7 electron in d orbital which will cause d- d transitionand hence further causes colour.

SC³⁺ = [ Ar ] 3d⁰

Here we can see that there is presence of 0 electron in d orbital hence there will be no d- d

transition and hence further no colour.

V=[ Ar ] 3d²

Here we can see that there is presence of 2 electron in d orbital which will cause d- d transition

and hence further causes colour.

Answer 2

Answer:

Explanation:

Scandium:

A chemical element with the symbol Sc and atomic number $21$ is called scandium. It has previously been categorized as a rare-earth element, along with yttrium and the lanthanides, and is a metallic, silvery-white d-block element. By spectral examination of the Scandinavian minerals euxenite and gadolinite, it was first identified in $1879$.

Scandium is present in most of the deposits of rare-earth and uranium compounds, but it is extracted from these ores in only a few mines worldwide. Because of the low availability and the difficulties in the preparation of metallic scandium, which was first done in $1937$, applications for scandium were not developed until the $1970$s, when the positive effects of scandium on aluminium alloys were discovered, and its use in such alloys remains its only major application. The global trade of scandium oxide is $15-20$ tonnes per year.

The properties of scandium compounds are intermediate between those of aluminium and yttrium. A diagonal relationship exists between the behavior of magnesium and scandium, just as there is between beryllium and aluminium. In the chemical compounds of the elements in group $3$, the predominant oxidation state is $+3$.

As a result, Sc$3+$ is colourless because it has no unpaired electrons, and Ti$3+$ is coloured because it has one unpaired electron.

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