Periodic Table & Periodicity — Page 3 | JEE Chemistry

Q21

The electronic configurations of bivalent europium and trivalent cerium are (atomic number : Xe = 54, Ce = 58, Eu = 63)

A [Xe] 4f7 6s2 and [Xe] 4f2 6s2

B [Xe] 4f2 and [Xe] 4f7

C [Xe] 4f4 and [Xe] 4f9

D [Xe] 4f7 and [Xe] 4f1

Correct Answer

Option D

Solution

Eu2+ : [xe] 4f7 Ce3+ : [xe] 4f1

Q22

The increasing order of the atomic radii of the following elements is :- (a) C (b) O (c) F (d) Cl (e) Br

A (a) < (b) < (c) < (d) < (e)

B (c) < (b) < (a) < (d) < (e)

C (b) < (c) < (d) < (a) < (e)

D (d) < (c) < (b) < (a) < (e)

Correct Answer

Option B

Solution

Generally in a period Left to Right Atomic radius decrease.

In a Group Top to Bottom Atomic radius increase.

Atomic radius order : Br > Cl > C > O > F

Q23

Number of elements from the following that CANNOT form compounds with valencies which match with their respective group valencies is ________. B, C, N, S, O, F, P, Al, Si

A 7

B 3

C 5

D 6

Correct Answer

Option B

Solution

N, F and O will not satisfy the given condition.

Q24

The alloy used in the construction of aircrafts is :

A Mg – Zn

B Mg – Al

C Mg – Mn

D Mg – Sn

Correct Answer

Option B

Solution

An alloy of Mg and Al called magnalium is used in manufacturing of aircraft due to its light weight and high strength.

Q25

The correct order of the first ionization enthalpy is

A

\mathrm{Ga}>\mathrm{Al}>\mathrm{B}

B

\mathrm{Tl}>\mathrm{Ga}>\mathrm{Al}

C

\mathrm{Al}>\mathrm{Ga}>\mathrm{Tl}

D

\mathrm{B}>\mathrm{Al}>\mathrm{Ga}

Correct Answer

Option B

Solution

I.

\mathrm{E}_1

of

\mathrm{TI}=589 \mathrm{~kJ} / \mathrm{mol}

I.

\mathrm{E}_1

of

\mathrm{Ga}=579 \mathrm{~kJ} / \mathrm{mol}

I.

\mathrm{E_1}

of

\mathrm{Al}=577 \mathrm{~kJ} / \mathrm{mol}

Q26

Among the statements (I – IV), the correct ones are: (I) Be has smaller atomic radius compared to Mg. (II) Be has higher ionization enthalpy than Al. (III) Charge/radius ratio of Be is greater than that of Al. (IV) Both Be and Al form mainly covalent compounds.

A (I), (II) and (IV)

B (II), (III) and (IV)

C (I), (III) and (IV)

D (I), (II) and (III)

Correct Answer

Option A

Solution

Be < Mg (atomic radius) Be > Al (I.E1 greater than Al because of fully filled valence shell of Be) Charge/radius ratio of Be is less than that of Al.

Both Be and Al form mainly covalent compound.

Q27

Which one of the following alkaline earth metal sulphates has its hydration enthalpy greater than its lattice enthalpy?

A BeSO4

B BaSO4

C SrSO4

D CaSO4

Correct Answer

Option A

Solution

In alkaline earth metals, ionic size increases down the group.

The lattice energy remains constant because sulphate ion is so large, so that small change in cationic size does not make any difference.

On moving down the group the degree of hydration of metal ions decreases very much leading to decrease in solubility.

$\therefore$

\,\,\,BeS{O_4} > MgS{O_4} > CaS{O_4} > SrS{O_4} > BaS{O_4}

Q28

Alkali metal from the following with least melting point is :

A

\mathrm{Rb}

B

\mathrm{Na}

C

\mathrm{K}

D

\mathrm{Cs}

Correct Answer

Option D

Solution

The alkali metals are the elements in Group 1 of the periodic table.

They are lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs).

The melting point of these metals decreases down the group as the size of the atoms increases.

This is because the metallic bonding weakens as the atomic size increases, resulting in a lower melting point.

Therefore, the alkali metal with the lowest melting point is cesium (Cs).

So, the correct option is Option D, Cs.

Q29

The element with Z = 120 (not yet discovered) will be an/a -

A Alkaline earth metal

B Alkali metal

C Transition metal

D Inner transition metal

Correct Answer

Option A

Solution

Electronic configuration of element Og (118) is [Rn] 5f146d 107s 27p6, where Og is oganesson.

[Og118] 8s2 is configuration for Z = 120, As per the configuration it is in IInd group.

Thus, element with Z = 120 will be an alkaline earth metal.

Q30

The correct option with respect to the Pauling electronegativity values of the element is :

A Ga < Ge

B Si < Al

C Te > Se

D P > S

Correct Answer

Option A

Solution

Electronegativity increases from left to right in a period and decreases down the group.

The correct orders are Si > Al, Ga < Ge, Te < Se and P < S.