Periodic Table & Periodicity — Page 17 | JEE Chemistry

Q161

Which one of the following compounds is used as a chemical in certain type of fire extinguishers?

A Baking soda

B Soda ash

C Washing soda

D Caustic soda

Correct Answer

Option A

Solution

Baking soda

\left(\mathrm{NaHCO}_{3}\right)

is used in certain type of fire extinguishers because it decomposes at high temperature to produce

\mathrm{CO}_{2}

which extinguishes fire

2 \mathrm{NaHCO}_{3}(\mathrm{~s}) \stackrel{\Delta}{\longrightarrow} \mathrm{Na}_{2} \mathrm{CO}_{3}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{O} \uparrow + \,\mathrm{CO}_{2} \uparrow

Q162

Choose the correct statement(s) : A. Beryllium oxide is purely acidic in nature. B. Beryllium carbonate is kept in the atmosphere of

\mathrm{CO_2}

. C. Beryllium sulphate is readily soluble in water. D. Beryllium shows anomalous behaviour. Choose the correct answer from the options given below :

A A only

B B, C and D only

C A, B and C only

D A and B only

Correct Answer

Option B

Solution

A.

Beryllium oxide is amphoteric in nature.

B.

Beryllium carbonate is kept in the atmosphere of CO2 because it is thermally less stable.

C.

Beryllium sulphate is readily soluble in water due to high degree of hydration.

D.

Beryllium shows anomalous behaviour due to small size, high ionization energy and high value of $\phi$ (polarising power).

Q163

Choose the correct order of density of the alkali metals :

A Li < K < Na < Rb < Cs

B Li < Na < K < Rb < Cs

C Cs < Rb < K < Na < Li

D Li < Na < K < Cs < Rb

Correct Answer

Option A

Solution

The increasing order of density of alkali metals as

\underset{0.53}{\mathrm{Li}}<\underset{0.86}{\mathrm{~K}}<\underset{0.97}{\mathrm{Na}}<\underset{1.53}{\mathrm{Rb}}<\underset{1.87}{\mathrm{Cs}} \quad\text{ (in } \mathrm{g}{/ \mathrm{dm}^{3} \text{ ) }}

' $\mathrm{K}$ ' metal has less density as compare to ' $\mathrm{Na}$ ' metal.

Q164

The correct order of density is :

A Be > Mg > Ca > Sr

B Sr > Ca > Mg > Be

C Sr > Be > Mg > Ca

D Be > Sr > Mg > Ca

Correct Answer

Option C

Solution

Density of

\mathrm{Sr}=2.63 \mathrm{~g} / \mathrm{cm}^{3}

Density of

\mathrm{Be}=1.84 \mathrm{~g} / \mathrm{cm}^{3}

Density of

\mathrm{Mg}=1.74 \mathrm{~g} / \mathrm{cm}^{3}

Density of

\mathrm{Ca}=1.55 \mathrm{~g} / \mathrm{cm}^{3}

Q165

Reaction of

\mathrm{BeCl}_{2}

with

\mathrm{LiAlH}_{4}

gives : (A)

\mathrm{AlCl}_{3}

(B)

\mathrm{BeH}_{2}

(C)

\mathrm{LiH}

(D)

\mathrm{LiCl}

(E)

\mathrm{BeAlH}_{4}

Choose the correct answer from options given below :

A (A), (D) and (E)

B (A), (B) and (D)

C (D) and (E)

D (B), (C) and (D)

Correct Answer

Option B

Solution

2 \mathrm{BeCl}_{2}+\mathrm{LiAlH}_{4} \rightarrow 2 \mathrm{BeH}_{2}+\mathrm{LiCl}+\mathrm{AlCl}_{3}

Q166

The metal that has very low melting point and its periodic position is closer to a metalloid is :

A Al

B Ga

C Se

D In

Correct Answer

Option B

Solution

Among the given elements, Gallium has the lowest melting point, Gallium is also close to a metalloid

Q167

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R. Assertion A:

\mathrm{LiF}

is sparingly soluble in water. Reason R: The ionic radius of

\mathrm{Li}^{+}

ion is smallest among its group members, hence has least hydration enthalpy. In the light of the above statements, choose the most appropriate answer from the options given below.

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

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

C A is true but R is false.

D A is false but R is true.

Correct Answer

Option C

Solution

LiF is sparingly soluble in water. The low solubility of LiF in water is due to its high lattice enthalpy (Since

\mathrm{Li}^{+}

and

\mathrm{F}^{-}

are small in size). Also, due to small size of

\mathrm{Li}^{+}

, its hydration enthalpy is high. Hence, Assertion is true but Reason is false

Q168

An element A of group 1 shows similarity to an element B belonging to group 2. If A has maximum hydration enthalpy in group 1 then B is :

A Mg

B Be

C Ca

D Sr

Correct Answer

Option A

Solution

Li+ $\to$ Maximum hydration enthalpy in group 1 due to small size. So ‘B’ is Mg.

Q169

Which of the following statement is incorrect?

A Low solubility of LiF in water is due to its small hydration enthalpy.

B

\mathrm{KO}_{2}

is paramagnetic.

C Solution of sodium in liquid ammonia is conducting in nature.

D Sodium metal has higher density than potassium metal.

Correct Answer

Option A

Solution

Low solubility of LiF in water is due to the fact that though $\mathrm{Li}^{+}$ is having high hydration enthalpy but it has higher lattice enthalpy when present in LiF.

Due to higher lattice enthalpy its solubility is less.

Q170

The correct decreasing order for metallic character is :

A Na > Mg > Be > Si > P

B P > Si > Be > Mg > Na

C Si > P > Be > Na > Mg

D Be > Na > Mg > Si > P

Correct Answer

Option A

Solution

Metallic character increases top to bottom in group and decreases left to right in a period. $\mathrm{Mg}$ is from second group it will be less metallic than $\mathrm{Na}$ .

Be comes above $\mathrm{Mg}$ hence less metallic than Mg.

Si is more metallic than phosphorous.