1

### JEE Advanced 2020 Paper 2 Offline

Numerical
An acidified solution of potassium chromate was layered with an equal volume of amyl alcohol. When it was shaken after the addition of 1 mL of 3% H2O2, a blue alcohol layer was obtained. The blue colour is due to the formation of a chromium (VI) compound 'X'. What is the number of oxygen atoms bonded to chromium through only single bond in a molecule of X?

## Explanation

When a solution of K2CrO4 is treated with amyl alcohol and acidified H2O2, the layer of amyl alcohol turns blue because acidified H2O2 converts K2CrO4 to CrO5 to given the blue colouration,

The structure of CrO5 is :

Number of oxygen atom bonded with chromium with single bond is = 4.
2

### JEE Advanced 2018 Paper 1 Offline

Numerical
Among the species given below, the total number of diamagnetic species is _____________.

$$H$$ atom, $$N{O_2}$$ monomer, $${O_2}^ -$$ (superoxide), dimeric sulphur in vapor phase, $$M{n_3}{O_4},\,\,$$ $${\left( {N{H_4}} \right)_2}\left[ {FeC{l_4}} \right],$$ $${\left( {N{H_4}} \right)_2}\left[ {NiC{l_4}} \right],\,$$ $$\,{K_2}Mn{O_4},\,$$$${K_2}Cr{O_4}$$

## Explanation

Among the given species only K2CrO4 is diamagnetic as central metal atom Cr in it has [Ar]3d0 electronic configuration i.e., all paired electrons. The structure and oxidation state of central metal atom of this compound are as follows

Structure

Oxidation state Cr6+

Rest all the compounds are paramagnetic. Reasons for their paramagnetism are given below.

(i) H-atom have 1s1 electronic configuration i.e., 1 unpaired electron.

(ii) NO2 i.e.

in itself is an odd electron species.

(iii) O$$_2^ -$$ (Superoxide) has one unpaired electron in $$\pi$$* molecular orbital.

(iv) S2 in vapour phase has O2 like electronic configuration i.e., have 2 unpaired electrons in $$\pi$$* molecular orbitals.

(v) Mn3O4 has following structure

Thus, Mn is showing +2 and +4 oxidation states. The outermost electronic configuration of elemental Mn is 3d54s2. Hence, in both the above oxidation states it has unpaired electron as

(vi) (NH4)2FeCl4 has Fe as central metal atom with +2 oxidation state. The electronic configuration of Fe2+ in the complex is

(vii) (NH4)2NiCl4 has Ni as central metal atom with +2 oxidation state. The electronic configuration of Ni2+ in the complex is

(viii) In K2MnO4 central metal atom Mn has +6 oxidation state with following structure

Electronic configuration of Mn6+ is

3

### JEE Advanced 2014 Paper 1 Offline

Numerical
Among PbS, CuS, HgS, MnS, Ag2S, NiS, CoS, Bi2S3 nd SnS2 the total number of black coloured sulphides is

## Explanation

From qualitative analysis of the different metal ions it is found that PbS, CuS, HgS, Ag2S, NiS, CoS are black coloured

MnS$$-$$dirty pink/buff coloured, SnS2$$-$$yellow coloured, Bi2S3$$-$$brown/black (brownish black) coloured.

Hence, correct integer is (7).

#### Questions Asked from d and f Block Elements

On those following papers in Numerical
Number in Brackets after Paper Indicates No. of Questions
JEE Advanced 2020 Paper 2 Offline (1)
JEE Advanced 2018 Paper 1 Offline (1)
JEE Advanced 2014 Paper 1 Offline (1)

### Joint Entrance Examination

JEE Main JEE Advanced WB JEE

### Graduate Aptitude Test in Engineering

GATE CSE GATE ECE GATE EE GATE ME GATE CE GATE PI GATE IN

NEET

Class 12