p-Block Elements — Page 3 | NEET Chemistry

Q21

20.0 g of a magnesium carbonate sample decomposes on heating to give carbon dioxide and 8.0 g magnesium oxide. What will be the percentage purity of magnesium carbonate in the sample? (At. wt. of Mg = 24)

A 96

B 60

C 84

D 75

Correct Answer

Option C

Solution

MgCO 3

\overset{\Delta}\longrightarrow

MgO + CO 2 84 g of MgCO 3 $\equiv$ 40 g of MgO $\therefore$ 20 g of MgCO 3 =

{{40} \over {84}} \times 20

= 9.52 g of MgO But Actual yield = 8 g of MgO $\therefore$ % purity =

{8 \over {9.52}} \times 100

= 84%

Q22

On heating which of the following releases CO 2 most easily?

A Na 2 CO 3

B MgCO 3

C CaCO 3

D K 2 CO 3

Correct Answer

Option B

Solution

Carbonates becomes more thermally stable down the group, Also, the alkali metal carbonate are more stable than alkaline earth metal carbonates.

Therefore MgCO 3 will leave CO 2 easily.

MgCO 3

\overset{\Delta}\longrightarrow

MgO + CO 2

Q23

The function of ''Sodium pump'' is a biological process operating in each and every cell of all animals. Which of the following biologically important ions is also a constituent of this pump?

A K +

B Fe 2+

C Ca 2+

D Mg 2+

Correct Answer

Option A

Solution

K + ion is a constituent of sodium pump.

Q24

Solubility of the alkaline earth metal sulphates in water decreases in the sequence

A Sr > Ca > Mg > Ba

B Ba > Mg > Sr > Ca

C Mg > Ca > Sr > Ba

D Ca > Sr > Ba > Mg

Correct Answer

Option C

Solution

Solubility of alkaline earth metal sulphates decreases down the group because hydration energy decreases.

Q25

In Castner-Kellner cell for production of sodium hydroxide

A brine is electrolyzed using graphite electrodes

B molten sodium chloride is electrolysed

C sodium amalgam is formed at mercury cathode

D brine is electrolyzed with Pt electrodes

Correct Answer

Option C

Solution

In Castner-Kellner cell, sodium amalgam is formed at mercury cathode.

Q26

Which one of the alkali metals, forms only, the normal oxide, M 2 O on heating in air?

A Rb

B K

C Li

D Na

Correct Answer

Option C

Solution

When alkali metals are heated in atmosphere of oxygen the alkali metals ignite and form oxides.

On combustion, Li forms Li 2 O, sodium gives the peroxide Na 2 O 2 while K and Rb give super oxides (MO 2 ).

Q27

The ease of adsorption of the hydrated alkali metal ions on an ion-exchange resins follows the order :

A Li + < K + < Na + < Rb +

B Rb + < K + < Na + < Li +

C K + < Na + < Rb + < Li +

D Na + < Li + < K + < Rb +

Correct Answer

Option B

Solution

All alkali metal salts are ionic (except Lithium) and soluble in water due to the fact that cations get hydrated by water molecules.

The degree of hydration depends upon the size of the cation.

Smaller the size of a cation, greater is its hydration energy.

Relative ionic radii : Li + < K + < Na + < Rb + Relative ionic radii in water or relative degree of hydration: Rb + < K + < Na + < Li +

Q28

Match with for the compositions of substances and select the correct answer using the code given above. <br><br> <table class=tg> <tbody><tr> <th class=tg-wv9z colspan=2><br>(Substances)</th> <th class=tg-wv9z colspan=2><br>(Composition)</th> </tr> <tr> <td class=tg-pjk9>

List - I		List - II
(A)	</td> <td class=tg-pjk9>Plaster of Pairs</td> <td class=tg-pjk9>	(i)	</td> <td class=tg-pjk9>CaSO<sub>4</sub> $\cdot$ 2H<sub>2</sub>O</td> </tr> <tr> <td class=tg-pjk9>
(B)	</td> <td class=tg-pjk9>Epsomite</td> <td class=tg-pjk9>	(ii)	</td> <td class=tg-pjk9>CaSO<sub>4</sub> $\cdot$ 1/2 H<sub>2</sub>O</td> </tr> <tr> <td class=tg-pjk9>
(C)	</td> <td class=tg-pjk9>Kieserite</td> <td class=tg-pjk9>	(iii)	</td> <td class=tg-pjk9>MgSO<sub>4</sub> $\cdot$ 7H<sub>2</sub>O</td> </tr> <tr> <td class=tg-pjk9>
(D)	</td> <td class=tg-pjk9>Gypsum</td> <td class=tg-pjk9>	(iv)	</td> <td class=tg-pjk9>MgSO<sub>4</sub> $\cdot$ H<sub>2</sub>O</td> </tr> <tr> <td class=tg-cyim></td> <td class=tg-cyim></td> <td class=tg-cyim>
()		(v)	</td> <td class=tg-cyim>CaSO<sub>4</sub></td> </tr> </tbody></table>

A (A)-(iii), (B)-(iv), (C)-(i), (D)-(ii)

B (A)-(ii), (B)-(iii), (C)-(iv), (D)-(i)

C (A)-(i), (B)-(ii), (C)-(iii), (D)-(iv)

D (A)-(iv), (B)-(iii), (C)-(ii), (D)-(i)

Correct Answer

Option B

Solution

(A) Plaster of paris = CaSO 4 .

{1 \over 2}

H 2 O (B) Epsomite = MgSO 4 .7H 2 O (C) Kieserite = MgSO 4 .H 2 O (D) Gypsum = CaSO 4 .2H 2 O

Q29

Which one of the following is present as an active ingredient in bleaching powder for bleaching action?

A CaOCl 2

B Ca(OCl) 2

C CaO 2 Cl

D CaCl 2

Correct Answer

Option B

Solution

Active ingredient in bleaching powder for bleaching action is Ca(OCl) 2 , i.e., calcium hypochlorite.

Q30

Which of the following compounds has the lowest melting point?

A CaCl 2

B CaBr 2

C CaI 2

D CaF 2

Correct Answer

Option C

Solution

As the covalent character in compound increases and ionic character decreases, melting point of the compound decreases.

So, CaI 2 has the highest covalent character and lowest melting point.