The reaction(s) involved in the preparation of potassium dichromate from iron chromite ore is/are:

The fusion of chromite ore (FeCr₂O₄) with Na₂CO₃ in air gives a yellow solution upon the addition of water. Subsequent treatment with H₂SO₄ produces an orange solution.

The yellow and orange colours, respectively, are due to the formation of:

1. Na₂CrO₄ and Na₂Cr₂O₇

2. Cr(OH)₃ and Na₂Cr₂O₇

3. Cr₂(CO₃)₃ and Fe₂(SO₄)₃

4. Cr(OH)₃ and Na₂CrO₄

When neutral or faintly alkaline ${\mathrm{KMnO}}_4$ is treated with potassium iodide, the iodide ion is converted into 'X'. The formula of 'X' is:

1. ${\mathrm{I}}_2$

2. ${\mathrm{IO}}_4^{-}$

3. ${\mathrm{IO}}_3^{-}$

4. ${\mathrm{IO}}^{-}$

HCl is not used to make the medium acidic in oxidation reaction of ${\mathrm{KMnO}}_4$ , because

A gas that can readily decolorize an acidified KMnO₄ solution is:

1. ${\mathrm{SO}}_2$

2. ${\mathrm{NO}}_2$

3. ${\mathrm{P}}_2{\mathrm{O}}_5$

4. ${\mathrm{CO}}_2$

CrO₄^2- (yellow) changes to Cr₂O₇^2- (orange) in pH = x and vice versa in pH = y.

The value of x and y will be:

1. 6, and 8

2. 6, and 5

3. 8, and 6

4. 7, and 7

Which of the following pairs of substances on reaction will not evolve gas?

1. Iron, and ${\mathrm{H}}_2{\mathrm{SO}}_4$ (aq)

2. Iron, and steam

3. Copper, and HCl(g)

4. Sodium, and ethyl alcohol

The oxidation state of chromium in the final product formed by the reaction between KI and acidified potassium dichromate solution will be:

1. +2

2. +3

3. +4

4. +6

Highest oxidation state of manganese in fluoride is +4 (Mn$F_4$) but the highest oxidation state in oxides is +7 (Mn₂O₇). The reason is :

When KMnO₄ solution is added to hot oxalic acid solution, the decolorization is slow in the beginning but becomes instantaneous after some time. This is because : 

1. ${\mathrm{Mn}}^{2+}$ acts as auto catalyst.

2. ${\mathrm{CO}}_2$ is formed.

3. Reaction is exothermic.

4. ${\mathrm{MnO}}_4^{-}$ catalyses the reaction.