The s-Block Elements Test 46

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The s-Block Elements Test 46

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Weekly Quiz Competition

Question 1
1 / -0

Smallest among these species is:

A
Hydrogen

B
Helium

C
Lithium

D
lithium ion

Solution
Question 2
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Which of the following equations is correct?

A
$$3LiNO_3\xrightarrow { heat } 2LiNO_2 + O_2$$

B
$$NaNO_3 + NaNH_2\xrightarrow { 80^o - 90^oC } 2NaOH +N_2O$$

C
Potassium formate is heated with free exposure to air. $$2HCOOK + O_2\longrightarrow K_2CO_3 + H_2O +CO_2$$

D
Solid $$KBrO_3$$ is heated with powdered charcoal. $$2KBrO_3 + 3C \longrightarrow 2KBr + 3CO_2$$

Solution
Question 3
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Which of the following represents calcium chlorite?

A
$$CaClO_2$$

B
$$Ca(ClO_4)_2$$

C
$$Ca(ClO_3)_2$$

D
$$Ca(ClO_2)_2$$

Solution
Question 4
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Compare $$x$$ and $$y$$ bond angle in above molecule.

A
$$x > y$$

B
$$y > x$$

C
$$x= y$$

D
none of these
Question 5
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The material used in solar cells contains:

A
Cs

B
Si

C
Sn

D
Ti

Solution

Solar cells can be classified into first, second and third-generation cells.

The first generation cells also called conventional, traditional or water-based cells are made of crystalline silicon, the commercially predominant PV (Poly-Voltaic) technology that includes materials such as polysilicon and monocrystalline silicon.

Silicon is a semi-conductor and is used in solar cells, sometimes doped.

Hence, the correct option is B .
Question 6
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Which of the following compounds is (are) not soluble in water?

A
$$Li_{2}CO_{3}$$

B
$$LiF$$

C
$$Li_{3}PO_{4}$$

D
$$All\ of\ these$$

Solution
Question 7
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Which of the following species does not exist under normal conditions?

A
$$ Be_2^+ $$

B
$$ Be_2 $$

C
$$ B_2 $$

D
$$ Li_2 $$

Solution

$$Bond$$ $$order$$ = $$1/2[\space Number\space of\space electrons\space in\space bonding\space orbital\space -\space Number\space of\space electrons\space in\space antibonding\space orbitals\space]$$
$$Bond$$ $$order$$ = $$1/2$$ [ $$N_b$$ - $$N_a$$ ]

(i) $$Be_2^+$$ :
Total valence electrons = 7
$$Configuration$$ :
$$[ \sigma(1s^2)\sigma^*(1s^2)\sigma(2s^2)\sigma^*(2s^1)]$$

$$Bond$$ $$order$$ = $$1/2[4-3]$$ = 0.5
$$Be_2^+$$ exist under normal condition.

(ii) $$Be_2$$ :
Total valence electrons = 8
$$Configuration$$ :
$$[ \sigma(1s^2)\sigma^*(1s^2)\sigma(2s^2)\sigma^*(2s^2)]$$

$$Bond$$ $$order$$ = $$1/2[4-4]$$ = 0
$$Be_2$$ does not exist.

(iii) $$B_2$$ :
Total valence electrons = 10
$$Configuration$$ :
$$[ \sigma(1s^2)\sigma^*(1s^2)\sigma(2s^2)\sigma^*(2s^2)\pi(2p_x^1)\pi(2p_y^1)]$$

$$Bond$$ $$order$$ = $$1/2[6-4]$$ = 1
$$B_2$$ is a stable molecule.

(iv) $$Li_2$$ :
Total valence electrons = 6
$$Configuration$$ :
$$[\sigma(1s^2)\sigma^*(1s^2)\sigma(2s^2)]$$

$$Bond$$ $$order$$ = $$1/2[4-2]$$ = 1
$$Li_2$$ is a stable molecule.

Hence the correct option is (B).
Question 8
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Select the correct statement:

A
Lithium carbonate is soluble in water

B
Potassium carbonate is soluble in water

C
Barium carbonate is soluble in water

D
Bicarbonate of lithium is insoluble in water
Solution
Lithium carbonate is a white solid, non-hygroscopic, poorly soluble in water, as well as most organic solvents. It is more soluble in cold water than hot water.
- Potassium carbonate $$(K_2CO_3)$$ is a white salt, soluble in water (insoluble in ethanol) which forms a strongly alkaline solution. It can be made as the product of potassium hydroxide's absorbent reaction with carbon dioxide.
Barium carbonate is a white powder. It is insoluble in water and soluble in most acids, with the exception of sulphuric acid.
Lithium bicarbonate is soluble in water.

Hence the correct answer is option B.
Question 9
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Which of the following does not exist in solid state?

A
$$LiHCO_{3}$$

B
$$NaHCO_{3}$$

C
$$KHCO_{3}$$

D
$$NH_{4}HCO_{3}$$

Solution

$$LiHCO_3$$ does not exist in solid state. This is because $$Li^+$$ cation has highest hydration enthalpy. So, they do not exist in solid state
Question 10
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Which of the following increases in magnitude as the atomic number of alkali metals increases?

A
Electronegativity

B
First ionisation potential

C
Ionic radius

D
Melting point

Solution