Periodic Table & Periodicity — Page 5 | NEET Chemistry

Q41

The incorrect relationship in the following pairs in relation to ionisation enthalpies is :

A

\mathrm{Mn}^{2+}<\mathrm{Fe}^{2+}

B

\mathrm{Mn}^{+}<\mathrm{Mn}^{2+}

C

\mathrm{Mn}^{+}<\mathrm{Cr}^{+}

D

\mathrm{Fe}^{2+}<\mathrm{Fe}^{3+}

Correct Answer

Option A

Solution

\mathrm{Mn}^{2+}:[\mathrm{Ar}] 3 \mathrm{~d}^5

Half filled stability More 1E than $\mathrm{Fe}^{2+}$

\mathrm{Fe}^{2+}:[\mathrm{Ar}] 3 \mathrm{~d}^6

Q42

The metal that cannot be obtained by electrolysis of an aqueous solution of its salts is :

A Cu

B Cr

C Ag

D Ca

Correct Answer

Option D

Solution

On electrolysis of aqueous solution of

s

-block elements

{H_2}

gas discharge at cathode. At cathode:

{H_2}O + {e^ - } \to {1 \over 2}{H_2} + O{H^ - }

Q43

The correct sequence of thermal stability of the following carbonates is :

A BaCO3 < SrCO3 < CaCO3 < MgCO3

B MgCO3 < CaCO3 < SrCO3 < BaCO3

C BaCO3 < CaCO3 < SrCO3 < MgCO3

D MgCO3 < SrCO3 < CaCO3 < BaCO3

Correct Answer

Option B

Solution

Stability of alkaline earth metal carbonates increases down the group as size of cation increases ans polarization decreases down the group : MgCO3 < CaCO3 < SrCO3 < BaCO3

Q44

The commercial name for calcium oxide is :

A Milk of lime

B Slaked lime

C Limestone

D Quick lime

Correct Answer

Option D

Solution

The commercial name of calcium oxide (CaO) is quick lime.

Q45

Reaction of BeO with ammonia and hydrogen fluoride gives A which on thermal decomposition gives

\mathrm{BeF_2}

and

\mathrm{NH_4F}

. What is 'A'?

A

\mathrm{(NH_4)Be_2F_5}

B

\mathrm{(NH_4)_2BeF_4}

C

\mathrm{(NH_4)BeF_3}

D

\mathrm{H_3NBeF_3}

Correct Answer

Option B

Solution

\mathrm{BeO}+\mathrm{NH}_{3}+\mathrm{HF} \longrightarrow\left(\mathrm{NH}_{4}\right)_{2} \underset{(\mathrm{A})}{\mathrm{BeF}_{4}} \stackrel{\Delta}{\longrightarrow} \mathrm{BeF}_{2}+\mathrm{NH}_{4} \mathrm{~F}

Compound $\mathrm{A}$ is $\left(\mathrm{NH}_{4}\right)_{2} \mathrm{BeF}_{4}$

Q46

The number of water molecules in gypsum, dead burnt plaster and plaster of Paris, respectively are :

A 2, 0 and 1

B 0.5, 0 and 2

C 5, 0 and 0.5

D 2, 0 and 0.5

Correct Answer

Option D

Solution

Gypsum

CaS{O_4}.2{H_2}O

Plaster of Paris

CaS{O_4}.{1 \over 2}{H_2}O

Dead burnt plaster

CaS{O_4}

Q47

In general, the properties that decrease and increase down a group in the periodic table, respectively, are :

A Atomic Radius and Electronegativity

B Electron Gain Enthalpy and Electronegativity.

C Electronegativity and Atomic Radius.

D Electronegativity and Electron Gain Enthalpy.

Correct Answer

Option C

Solution

Electronegativity decreases down the group because the increased number of energy levels puts the outer electrons very far away from the pull of nucleus.

Atomic radius increases down the group because the number of energy levels increases when you move down the group.

Each subsequent energy level is further from the molecules than the last.

That is why atomic radius increases down the group.

Q48

The ionic radii (in Å) of N3–, O2– and F– are respectively:

A 1.36, 1.71 and 1.40

B 1.71, 1.40 and 1.36

C 1.71, 1.36 and 1.40

D 1.36, 1.40 and 1.71

Correct Answer

Option B

Solution

Here all of them are isoelectric and for isoelectric species size of anion increases as negative charge increases.

So, correct order is : N3– > O2– > F– $\therefore$ Radius of N3– = 1.71 Å and Radius of O2– = 1.40 Å and Radius of F– = 1.36 Å

Q49

The ionic radii of K+, Na+, Al3+ and Mg2+ are in the order:

A Na+ < K+ < Mg2+ < Al3+

B Al3+ < Mg2+ < K+ < Na+

C Al3+ < Mg2+ < Na+ < K+

D K+ < Al3+ < Mg2+ < Na+

Correct Answer

Option C

Solution

Al3+, Mg2+ and Na+ are isoelectronic ionic species.

For monoatomic ionic isoelectronic species as positive charge increases ionic size decreases.

The order of size of Na+ & K+ is Na+ < K+ $\therefore$ Order of ionic radii is : Al3+ < Mg2+ < Na+ < K+

Q50

In which of the following pairs, electron gain enthalpies of constituent elements are nearly the same or identical? (A) Rb and Cs (B) Na and K (C) Ar and Kr (D) I and At Choose the correct answer from the options given below :

A (A) and (B) only

B (B) and (C) only

C (A) and (C) only

D (C) and (D) only

Correct Answer

Option C

Solution

$\mathrm{Rb} \,\& \,\mathrm{Cs}$ have nearly same electron gain enthalpy electron gain enthalpy $=-46\, \mathrm{kj} / \mathrm{ml}$ Ar & Kr have same $\Delta \mathrm{H}_{\mathrm{eq}} .$ Value is $+96 \,\mathrm{kj} / \mathrm{ml}$