Periodic Table & Periodicity — Page 20 | JEE Chemistry

Q191

Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R. Assertion A : Sodium is about 30 times as abundant as potassium in the oceans. Reason R : Potassium is bigger in size than sodium. In the light of the above statements, choose the correct answer from the options given below

A Both A and R are true but R is NOT the correct explanation of A

B A is false but R is true

C Both A and R are true and R is the correct explanation of A

D A is true but R is false

Correct Answer

Option C

Solution

Due to bigger size of potassium, it forms more efficient lattices as compared to sodium with silicates.

The abundance of sodium in ocean is more due to the more soluble nature of salt of sodium as compared to potassium salts.

Q192

For a good quality cement, the ratio of lime to the total of the oxides of

\mathrm{Si}, \mathrm{Al}

and

\mathrm{Fe}

should be as close as to :

A 3

B 2

C 1

D 4

Correct Answer

Option B

Solution

For good quality cement, the ratio of lime (CaO) to the sum of the oxides of silicon (SiO₂), aluminum (Al₂O₃), and iron (Fe₂O₃) should be approximately 2:1.

This proportion ensures that the cement has good strength and setting properties, as well as resistance to chemical attack.

Q193

Given below are two statements: Statement I : Lithium and Magnesium do not form superoxide Statement II : The ionic radius of

\mathrm{Li}^{+}

is larger than ionic radius of

\mathrm{Mg}^{2+}

In the light of the above statements, choose the most appropriate answer from the options given below :

A Statement I is incorrect but Statement II is correct

B Both Statement I and Statement II are incorrect

C Both Statement I and Statement II are correct

D Statement I is correct but Statement II is incorrect

Correct Answer

Option C

Solution

Statement I : "Lithium and Magnesium do not form superoxide" This statement is correct.

Lithium and magnesium are smaller in size compared to other elements in their respective groups.

Although lithium can form superoxide under certain conditions, in general, the smaller size of these two elements makes it harder for them to form stable superoxides.

Statement II : "The ionic radius of Li+ is larger than the ionic radius of Mg2+" This statement is still correct.

Despite both lithium and magnesium being small in size, when they lose electrons to form ions, the Mg2+ ion is smaller than the Li+ ion due to the loss of two electrons (and thus an energy level) in magnesium compared to the loss of one electron in lithium.

So, based on the information, the answer is : Option C : Both Statement I and Statement II are correct.

Q194

What is the purpose of adding gypsum to cement?

A To facilitate the hydration of cement

B To speed up the process of setting

C To give a hard mass

D To slow down the process of setting

Correct Answer

Option D

Solution

Cement is manufactured by heating limestone (calcium carbonate) with small amounts of other materials, such as clay, to a high temperature in a kiln in a process known as calcination, which produces clinker.

The clinker is then cooled and ground into a fine powder that we know as cement.

However, the clinker is highly reactive, and when mixed with water, it would harden immediately.

This would not be practical in a construction setting because it doesn't allow enough time for the cement mix to be poured, shaped, or smoothed out.

Gypsum ( $\mathrm{CaSO}_4 \cdot 2 \mathrm{H}_2 \mathrm{O}$ ) is added to this clinker before it's ground into cement.

The role of gypsum is to extend the time it takes for the cement to set, giving the workers enough time to work with the cement before it hardens.

The gypsum reacts with the clinker during the final grinding process, controlling the rate at which the cement will set.

If no gypsum was added, the cement would set as soon as water is added, making it almost impossible to use in construction.

Q195

The product, which is not obtained during the electrolysis of brine solution is :

A NaOH

B Cl

_2

C H

_2

D HCl

Correct Answer

Option D

Solution

The electrolysis of brine, which is a solution of sodium chloride (NaCl) in water, involves the migration of ions towards electrodes.

When an electric current is passed through the solution, positive sodium ions ( $Na^+$ ) move towards the cathode (negative electrode), and negative chloride ions ( $Cl^-$ ) move towards the anode (positive electrode).

At the same time, water ( $H_2O$ ), which also dissociates into $H^+$ and $OH^-$ ions, also contribute to the reactions at the electrodes.

At the anode, chloride ions are oxidized to chlorine gas: $2Cl^- \rightarrow Cl_2(g) + 2e^-$ At the cathode, water is reduced to hydrogen gas and hydroxide ions, instead of sodium ions being reduced to sodium metal.

This is because water is more easily reduced than sodium ions: $2H_2O + 2e^- \rightarrow H_2(g) + 2OH^-$ The sodium ions remain in the solution and combine with the hydroxide ions to form sodium hydroxide: $Na^+ + OH^- \rightarrow NaOH$ So the products of the electrolysis of brine are chlorine gas, hydrogen gas, and sodium hydroxide.

Hydrochloric acid (HCl) is not produced during this process because the hydrogen and chloride ions do not combine in the electrolyte solution to form HCl.

They are separately reduced and oxidized at the cathode and anode respectively.

Q196

Ion having highest hydration enthalpy among the given alkaline earth metal ions is :

A

\mathrm{Sr}^{2+}

B

\mathrm{Ca}^{2+}

C

\mathrm{Be}^{2+}

D

\mathrm{Ba}^{2+}

Correct Answer

Option C

Solution

Hydration enthalpy is the amount of energy released when one mole of gaseous ions is completely surrounded by water molecules.

The process is exothermic, hence the enthalpy change is negative.

Generally, smaller ions and ions with higher charge have larger hydration enthalpies due to the stronger attraction to the water molecules.

This is because the hydration enthalpy depends on the charge density of the ion.

Among the given options,

\mathrm{Be}^{2+}

is the smallest ion and it has the same charge as the other ions.

Hence, it has the highest charge density and will have the highest hydration enthalpy.

Q197

Structures of

\mathrm{BeCl}_{2}

in solid state, vapour phase and at very high temperature respectively are :

A Polymeric, Dimeric, Monomeric

B Dimeric, Polymeric, Monomeric

C Polymeric, Monomeric, Dimeric

D Monomeric, Dimeric, Polymeric

Correct Answer

Option A

Solution

$\mathrm{BeCl}_2$ forms a polymeric structure in the solid state due to coordination bonds formed by chlorine donating a lone pair of electrons to the beryllium atoms.

In the vapour phase at moderate temperatures, $\mathrm{BeCl}_2$ exists as a dimer, forming a bridge structure with two chlorine atoms connected to two beryllium atoms.

At very high temperatures, $\mathrm{BeCl}_2$ exists as monomers due to the high kinetic energy of the molecules, which overcomes the dimerisation tendency.

Q198

Match List I with List II. .tg .tg LIST I Alkali Metal LIST II Emission Wavelength in nm A. Li I. 589.2 B. Na II. 455.5 C. Rb III. 670.8 D. Cs IV. 780.0 Choose the correct answer from the options given below :

A (A)-(II), (B)-(IV), (C)-(III), (D)-(I)

B (A)-(III), (B)-(I), (C)-(IV), (D)-(II)

C (A)-(I), (B)-(IV), (C)-(III), (D)-(II)

D (A)-(IV), (B)-(II), (C)-(I), (D)-(III)

Correct Answer

Option B

Solution

To match List I (Alkali Metals) with List II (Emission Wavelength in nm), we need to know the characteristic emission lines of these elements.

Here is the information for the typical emission wavelengths: Lithium (Li): 670.8 nm Sodium (Na): 589.2 nm Rubidium (Rb): 780.0 nm Cesium (Cs): 455.5 nm Now let's match these with the given options: A.

Li (III): 670.8 nm B.

Na (I): 589.2 nm C.

Rb (IV): 780.0 nm D.

Cs (II): 455.5 nm Therefore, the correct answer is: Option B (A)-(III), (B)-(I), (C)-(IV), (D)-(II)

Q199

Match with : {O_7}$$

List - I		List - II
(B)	$N{a_2}O$	(I)	Amphoteric
(C)	$A{l_2}{O_3}$	(II)	Basic
(D)	${N_2}O$	(III)	Neutral
()		(IV)	Acidic

A (A) - (IV), (B) - (III), (C) - (I), (D) - (II)

B (A) - (IV), (B) - (II), (C) - (I), (D) - (III)

C (A) - (II), (B) - (IV), (C) - (III), (D) - (I)

D (A) - (I), (B) - (II), (C) - (III), (D) - (IV)

Correct Answer

Option B

Solution

(A) Cl2O7 → Acidic (B) Na2O → Basic (C) Al2O3 → Amphoteric (D) N2O → Neutral Oxides of metals are basic in nature whereas oxides of non-metals are acidic in nature.

N2O is a neutral oxide.

Q200

Match with . }$$

List - I		List - II
(B)	$\mathrm{Mn^+}$	(I)	$\mathrm{3d^8}$
(C)	$\mathrm{Ni^{+2}}$	(II)	$\mathrm{3d^34s^1}$
(D)	$\mathrm{V^+}$	(III)	$\mathrm{3d^4}$
()		(IV)	$\mathrm{3d^54s^1}$

A (A)-(III), (B)-(IV), (C)-(I), (D)-(II)

B (A)-(I), (B)-(II), (C)-(III), (D)-(IV)

C (A)-(IV), (B)-(III), (C)-(I), (D)-(II)

D (A)-(II), (B)-(I), (C)-(IV), (D)-(III)

Correct Answer

Option A

Solution

\begin{gathered} { }_{24} \mathrm{Cr} \rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^5 4 \mathrm{~s}^1 ; \mathrm{Cr}^{2+} \rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^4 \\ { }_{25} \mathrm{Mn} \rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^5 4 \mathrm{s}^2 ; \mathrm{Mn}^{+} \rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^5 4 \mathrm{s}^1 \\ { }_{28} \mathrm{Ni} \rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^8 4 \mathrm{s}^2 ; \mathrm{Ni}^{2+} \rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^8 \\ { }_{23} \mathrm{V} \rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^3 4 \mathrm{s}^2 ; \mathrm{V}^{+} \rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^3 4 \mathrm{s}^1 \end{gathered}