Periodic Table & Periodicity — Page 18 | JEE Chemistry

Q171

Statement I : An alloy of lithium and magnesium is used to make aircraft plates. Statement II : The magnesium ions are important for cell-membrane integrity. In the light the above statements, choose the correct answer from the options given below :

A Both Statement I and Statement II are true

B Both Statement I and Statement II are false

C Statement I is true but Statement II is false

D Statement I is false but Statement II is true

Correct Answer

Option B

Solution

Alloy of Li and Mg is used to make armour plates and not aircraft plates.

Calcium plays important roles in neuromuscular function, interneuronal transmission and cell membrane integrity .

Q172

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : Gypsum is used for making fireproof wall boards. Reason (R) : Gypsum is unstable at high temperatures. In the light of the above statements, choose the correct answer from the options given below :

A Both (A) and (R) are correct but (R) is not the correct explanation of (A)

B Both (A) and (R) are correct and (R) is the correct explanation of (A)

C (A) is correct but (R) is not correct

D (A) is not correct but (R) is correct

Correct Answer

Option A

Solution

"Both (A) and (R) are correct but (R) is not the correct explanation of (A)" is the correct answerGypsum is indeed used for making fireproof wall boards, but the reason given in (R) that gypsum is unstable at high temperatures is not the correct explanation for why it is used for this purpose.

Instead, gypsum is fire-resistant because it does not support combustion and does not emit toxic fumes when exposed to fire.

Q173

The element playing significant role in neuromuscular function and interneuronal transmission is :

A Be

B

\mathrm{Ca}

C

\mathrm{Mg}

D

\mathrm{Li}

Correct Answer

Option B

Solution

Calcium plays important role in neuromuscular function, interneuronal transmission, cell membrane etc.

Q174

Which of the following reaction is correct?

A

4 \mathrm{LiNO}_{3} \stackrel{\Delta}{\longrightarrow} 2 \mathrm{Li}_{2} \mathrm{O}+4 \mathrm{NO}_{2}+\mathrm{O}_{2}

B

2 \mathrm{LiNO}_{3} \longrightarrow 2 \mathrm{Li}+2 \mathrm{NO}_{2}+\mathrm{O}_{2}

C

4 \mathrm{LiNO}_{3} \stackrel{\Delta}{\longrightarrow} 2 \mathrm{Li}_{2} \mathrm{O}+2 \mathrm{~N}_{2} \mathrm{O}_{4}+\mathrm{O}_{2}

D

2 \mathrm{LiNO}_{3} \stackrel{\Delta}{\longrightarrow} 2 \mathrm{NaNO}_{2}+\mathrm{O}_{2}

Correct Answer

Option A

Solution

\mathrm{4LiNO_3}

\overset{{\mathrm{Heat}}}\longrightarrow

\mathrm{2Li_2O+4NO_2+O_2}

\mathrm{LiNO_3}

on heating produces

\mathrm{Li_2O,NO_2}

and

\mathrm{O_2}

Q175

Lithium aluminium hydride can be prepared from the reaction of :

A

\mathrm{LiCl}

and

\mathrm{Al_2H_6}

B

\mathrm{LiH}

and

\mathrm{Al}(\mathrm{OH})_{3}

C

\mathrm{LiH}

and

\mathrm{Al}_{2} \mathrm{Cl}_{6}

D

\mathrm{LiCl}, \mathrm{Al}

and

\mathrm{H}_{2}

Correct Answer

Option C

Solution

\mathrm{8LiH+Al_2Cl_6\to2LiAlH_4+6LiCl}

Q176

The alkaline earth metal sulphate(s) which are readily soluble in water is/are : A.

\mathrm{BeSO}_{4}

B.

\mathrm{MgSO}_{4}

C.

\mathrm{CaSO}_{4}

D.

\mathrm{SrSO}_{4}

E.

\mathrm{BaSO}_{4}

Choose the correct answer from the options given below :

A A and B

B B and C

C B only

D A only

Correct Answer

Option A

Solution

BeSO

_4

and MgSO

_4

are readily soluble in water.

Q177

The correct order of hydration enthalpies is (A) K

^+

(B) Rb

^+

(C) Mg

^{2+}

(D) Cs

^+

(E) Ca

^{2+}

Choose the correct answer from the options given below :

A E > C > A > B > D

B C > A > E > B > D

C C > E > A > D > B

D C > E > A > B > D

Correct Answer

Option D

Solution

Hydration enthalpy $\propto$ charge density Charge density means

{{Magnitude\,of\,Charge} \over {Ionic\,Radius}}

. $\therefore$ The correct order of charge density is

\mathrm{Mg}^{2+}>\mathrm{Ca}^{2+}>\mathrm{K}^{+}>\mathrm{Rb}^{+}>\mathrm{Cs}^{+}

$\therefore$ The order of hydration enthalpy

C>E>A>B>D

Q178

Which one among the following metals is the weakest reducing agent?

A K

B Na

C Li

D Rb

Correct Answer

Option B

Solution

Sodium has the lowest oxidation potential in alkali metals. Hence it is the weakest reducing agent among alkali metals.

Q179

Which of the following represents the correct order of metallic character of the given elements?

A K < Mg < Be < Si

B Si < Be < Mg < K

C Be < Si < Mg < K

D Be < Si < K < Mg

Correct Answer

Option B

Solution

Metallic character of an element is directly proportional to its electropositivity.

Of the given elements silicon is least electro positive and potassium is most electropositive whereas beryllium and magnesium have intermediate values in the increasing order.

Therefore, correct order of metallic character is $\mathrm{Si} < \mathrm{Be} < \mathrm{Mg} < \mathrm{K}$ .

Q180

Number of water molecules in washing soda and soda ash respectively are :

A 1 and 0

B 10 and 1

C 1 and 10

D 10 and 0

Correct Answer

Option D

Solution

Washing soda is a hydrated form of sodium carbonate, with the chemical formula Na2CO3·10H2O.

This means that each molecule of washing soda contains 10 water molecules.

Soda ash is the anhydrous form of sodium carbonate, with the chemical formula Na2CO3.

This means that it does not contain any water molecules.

Soda ash is typically produced by heating washing soda to drive off the water molecules.

Washing soda can be produced by dissolving soda ash in water and then recrystallizing it.

The correct answer is Option D: 10 and 0.