The d- and f- Block Elements Test

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The d- and f- Block Elements Test - 68

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Weekly Quiz Competition

Question 1
1 / -0

What are the species A and B in the following.

$$ CrO_3 + H_2O \rightarrow A \xrightarrow{OH^-} B $$

A
$$ H_2CrO_4 , H_2Cr_2O_7 $$

B
$$ H_2Cr_2O_7 , Cr_2O_3 $$

C
$$ CrO_4^{2-} , Cr_2O_7^{-2} $$

D
$$ H_2Cr_2O_7 , CrO_4^{2-} $$

Solution

$$CrO_3$$ dissolves in water to produce orange colored acidic solution ($$Cr_2O_7^{2-}+2H^+$$).

$$2CrO_3+H_2O\rightarrow H_2Cr_2O_7$$

$$Cr_2O_7^{2-}+2OH^-\rightarrow 2CrO_4^{2-}+H_2O$$

Therefore, A = $$H_2Cr_2O_7$$, B = $$CrO_4^{2-}$$

Hence, the correct option is (D).
Question 2
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Maximum magnetic moments of $$ Cr (Z = 24), Mn^{+} (Z=25),$$ and $$Fe^{2+} (Z=26), $$ are x, y, and z. They are in order:

A
x < y < z

B
x = z <y

C
z < x = y

D
x = y = z
Question 3
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Chloro compound of vandium has only spin magnetic moment of 1.73 BM. This vanadium chloride has the formula (at.no V = 23)

A
$$ VCl_4 $$

B
$$ VCl_3 $$

C
$$ VCl_2 $$

D
$$ VCl_5 $$

Solution
Question 4
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Calomel $$ (Hg_2Cl_2) $$ on reaction with ammonium hydroxide gives:

A
$$HgO$$

B
$$ Hg_2O $$

C
$$ NH_2-Hg-Hg-Cl $$

D
$$ Hg NH_2Cl $$

Solution
Question 5
1 / -0

The magnetic moment is associated with its spin angular momentum and orbital angular momentum,spin only magnetic value of $$ Cr^{3+} $$ ion is.......

A
2.87 B.M

B
3.87 B.M

C
3.47 B.M

D
3.57 B.M

Solution
Question 6
1 / -0

An aqueous solution of $$ FeSO_4.Al_2(SO_4)_3 $$ and chrome alum is heated with excess of $$ Na_2O_2 $$ and filtered. The materials obtained are:

A
A colourless filtrate and a green residue

B
A yellow filtrate and a green residue

C
A yellow filtrate and a brown residue

D
A green filtrate and a brown residue

Solution

In the presence of peroxide, chromium ions are oxidised to chromate ions which give a yellow filtrate. Ferric ions from brown precipitate of $$ Fe(OH)_3. $$
Question 7
1 / -0

On hearting ammonium dichromate the gas enolved is:

A
Oxygen

B
Ammonia

C
Nitrous oxide

D
Nitrogen

Solution
Question 8
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$$ (NH_4)_2 Cr_2 O_7 $$ on heating gives a gas which is also given by:

A
Heating $$ NH_4NO_2 $$

B
Heating $$ NH_4NO_3 $$

C
$$ Mg_3N_2 + H_2O $$

D
Na(comp) + $$ H_2O_2 $$

Solution
Question 9
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Comprehension - 2
Potassium permanganate is prepared from the mineral pyrolusire $$ MnO_2 $$. Its crystal have deep purple color.It acts as an oxidizing agent in the netural,alkaline as well as acidic medium.In acidic medium,it is used in volumetric analysis for the estimation for ferrous salts,oxalates, etc.The titartion are carried out in the presence of $$ H_2SO_4 $$. However before using it as a titrant,it is first standardized with standard oxalic acid solution or Mohr salt solution.In one of the experiments on 13.4 g of dry pure sodium oxalate (molar mass = $$ 134 g mol^{-1} ) $$
was disolved in 100 mL of distilled water and then 100 mL of distilled water and then 100 mL of $$ 2.M H_2 SO_4 $$ were added.The solution was cooled to $$ 25.30^oC $$.Now to this solution 0.1 M $$ KMnO_4 $$Solution was added till a very faints pink color persisted.
(6) The purple color of $$ K_2 MnO_4 $$ is due to :

A
Incomplete d-subshell

B
Ionic nature of $$ KMnO_4 $$

C
Charge transfer

D
Resonance in $$ MnO^-_4 $$

Solution
Question 10
1 / -0

The radius of $$ La^{3+} $$ (At . No of $$La =57$$ ) is $$ 1.06 \mathring{A} $$ which one of the following given values will be closest to the radius of $$ Lu^{3+}$$ (at no. of $$Lu = 71$$ ) ?

A
$$ 1.40 \mathring{A} $$

B
$$ 1.06 \mathring{A} $$

C
$$ 0.85 \mathring{A} $$

D
$$ 1.60 \mathring{A} $$

Solution

A reduction in atomic/ionic size with increase in atomic number is a characteristic of lanthanoids. Hence, the ionic radius of Lu3+ will be smaller than the ionic radius of La3+ It will be less than 1.06 Å. Hence, the option C, 0.85 Å is the correct answer.