Periodic Table & Periodicity — Page 24 | JEE Chemistry

Q231

On combustion of Li, Na and K in excess of air, the major oxides formed, respectively, are :

A Li2O, Na2O2 and K2O

B Li2O2, Na2O2 and K2O2

C Li2O, Na2O2 and KO2

D Li2O, Na2O and K2O2

Correct Answer

Option C

Solution

4Li + O2 $\to$ 2Li2O 2Na + O2 $\to$ Na2O2 K + O2 $\to$ KO2

Q232

In general the property (magnitudes only) that show an opposite trend in comparison to other properties across a period is

A Electron gain enthalpy

B Electronegativity

C Ionization enthalpy

D Atomic radius

Correct Answer

Option D

Solution

Across a period (left to right) in the periodic table : Ionization enthalpy tends to increase Electron gain enthalpy (in magnitude) tends to increase (more negative values) Electronegativity tends to increase Atomic radius tends to decrease Hence, atomic radius shows the opposite trend compared to the other three properties.

Therefore, the correct answer is (D) Atomic radius.

Q233

Identify the elements X and Y using the ionisation energy values given below : Ionization energy (kJ/mol) 1

{st}

2

{nd}

X 495 4563 Y 731 1450

A X = F; Y = Mg

B X = Mg; Y = F

C X = Na; Y = Mg

D X = Mg; Y = Na

Correct Answer

Option C

Solution

Due to 2p6, noble gas electronic configuration, the second ionisation enthalpy of Na is very high.

That’s why has large difference between IE1, and IE2 Mg+ is 2p6, 3s1.

After the loss of one electron, Mg+ will be formed with noble gas electronic configuration.

That’s why has less difference between I.E1 and I.E2, but it's I.E3 is very high.

Q234

The absolute value of the electron gain enthalpy of halogens satisfies :

A Cl > Br > F > I

B Cl > F > Br > I

C I > Br > Cl > F

D F > Cl > Br > I

Correct Answer

Option B

Solution

The magnitude of electron gain enthalpy of halogen atoms down the group show abnormal behavior.

The |ΔHeg| of F is lower than that of Cl due to its smaller size.

The incoming electron experiences higher repulsive force due to valence electrons of F than Cl.

The correct order is Cl > F > Br > I.

Q235

The ionic radius of Na+ ions is 1.02

\mathop A\limits^o

. The ionic radii (in

\mathop A\limits^o

) of Mg2+ and Al3+, respectively, are

A 1.05 and 0.99

B 0.72 and 0.54

C 0.85 and 0.99

D 0.68 and 0.72

Correct Answer

Option B

Solution

The ionic radii (in

\mathop A\limits^o

) of

\text{Mg}^{2+}

and

\text{Al}^{3+}

, respectively, are: Option B:

0.72 \mathop A\limits^o

for

\text{Mg}^{2+}

0.54 \mathop A\limits^o

for

\text{Al}^{3+}

Q236

The metallic sodium disolves in liquid ammonia to form a deep blue coloured solution. The deep blue colour is due to formation of :

A solvated electron,

e(NH_3)^-_x

B solvated atomic sodium, Na(NH3)y

C (Na+ + Na-)

D NaNH2 + H2

Correct Answer

Option A

Solution

The alkali metals dissolve in liquid ammonia without evolution of hydrogen.

The metal loses electrons and combine with ammonia molecule.

M \to {M^ + }\,\,

(in liquid ammonia)

\,\, + {E^ - }\,\,

(ammoniated)

\,\,M + (x + y)N{H_3}

\to {\left[ {M{{(N{H_3})}_x}} \right]^ + }\mathop { + {e^ - }{{\left( {N{H_3}} \right)}_y}}\limits_{Solvated\,\,\,\,electron}

It is ammoniated electron which is responsible for color.

Q237

In curing cement plasters water is sprinkled from time to time. This helps in :

A developing interlocking needle like crystals of hydrated silicates

B hydrating sand and gravel mixed with cement

C converting sand into silicic acid

D keeping it cool

Correct Answer

Option A

Solution

Setting of cement is exothermic process which develops interlocking crystals of hydrated silicates

Q238

Given below are two statements : Statement I : None of the alkaline earth metal hydroxides dissolve in alkali. Statement II : Solubility of alkaline earth metal hydroxides in water increases down the group. In the light of the above statements, choose the most appropriate answer from the options given below :

A Statement I is correct but Statement II is incorrect.

B Statement I is incorrect but Statement II is correct.

C Statement I and Statement II both are incorrect.

D Statement I and Statement II both are correct.

Correct Answer

Option B

Solution

Statement - I is incorrect Be(OH)2 dissolve in alkali due to it's amphoteric nature.

Statement - II is correct Solubility of alkaline earth metal hydroxide in water increases down the group due to rapid decreases in lattice energy as compared to hydration energy.

Q239

Inert gases have positive electron gain enthalpy. Its correct order is :

A He < Ne < Kr < Xe

B He < Xe < Kr < Ne

C Xe < Kr < Ne < He

D He < Kr < Xe < Ne

Correct Answer

Option B

Solution

.tg .tg $\begin{gathered}\text{ Electron } \\\text{ gain }\end{gathered}$ $\mathrm{He}$ $\mathrm{Ne}$ $\mathrm{Ar}$ $\mathrm{Kr}$ $\mathrm{Xe}$ $\begin{gathered}\text{ Enthalpyl } / \\\mathrm{kJ} ~\mathrm{mol}^{-1}\end{gathered}$ 48 116 96 96 77

Q240

Consider the following elements

\mathrm{In}, \mathrm{Tl}, \mathrm{Al}, \mathrm{Pb}, \mathrm{Sn}

and Ge . The most stable oxidation states of elements with highest and lowest first ionisation enthalpies, respectively, are

A +4 and +1

B +4 and +3

C +1 and +4

D +2 and +3

Correct Answer

Option B

Solution

Among $\mathrm{Al}, \mathrm{In}, \mathrm{Tl}, \mathrm{Ge}, \mathrm{Sn}, \mathrm{Pb}$ , the metal having highest $\mathrm{IE}_1$ is Ge and lowest $\mathrm{IE}_1$ is $\mathrm{In}$ .

Most stable oxidation state of Ge is +4 and In is +3 .