1
MCQ (Single Correct Answer)

JEE Main 2016 (Online) 10th April Morning Slot

The transition metal ions responsible for color in ruby and emerald are, respectively :
A
Cr3+   and   Co3+
B
Co3+    and    Cr3+
C
Co3+    and    Co3+
D
Cr3+    and    Cr3+
2
MCQ (Single Correct Answer)

JEE Main 2017 (Offline)

In the following reactions, ZnO is respectively acting as a/an:

(a) ZnO + Na2O $$\to$$ Na2ZnO2

(b) ZnO + CO2 $$\to$$ ZnCO3
A
base and base
B
acid and acid
C
acid and base
D
base and acid

Explanation

Zinc oxide (ZnO) when react with Na2O it act as acid while with CO2 it act as base. Therefore, it is an amphoteric oxide.

(a) ZnO + Na2O $$\to$$ Na2ZnO2
     Acid      Base          Salt

(b) ZnO + CO2 $$\to$$ ZnCO3
     Base      Acid       Salt
3
MCQ (Single Correct Answer)

JEE Main 2017 (Online) 9th April Morning Slot

Which of the following ions does not liberate hydrogen gas on reaction with dilute acids ?
A
Ti2+
B
V2+
C
Cr2+
D
Mn2+

Explanation

The third ionisation energy of Mn is too high due to stable half filled 3d-orbital. Hence, it cannot further get oxidised to liberate hydrogen.
4
MCQ (Single Correct Answer)

JEE Main 2018 (Online) 16th April Morning Slot

When XO2 is fused with an alkali metal hydroxide in presence of an oxidizing agent such as KNO3 ; a dark green product is formed which disproportioates in acidic solution to afforda dark purple solution. X is :
A
Ti
B
V
C
Cr
D
Mn

Explanation

X is Mn.

MnO2  +  2KOH  +  KNO3  $$ \to $$  K2MnO4  +  KNO2  +  H2O

Here   K2MnO4  is dark green.

3MnO4$$-$$2  +  4H+  $$ \to $$  2MnO4$$-$$  +  MnO2  +  2H2O

In acidic solution, K2MnO4 changes to dark purple solution of KMnO4.

Questions Asked from d and f Block Elements

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