Oxidizing Reducing Agents

Oxidation numbers of P in ${\mathrm{PO}}_4^{3-}$, of S in ${\mathrm{SO}}_4^{2-}$ and that of Cr in ${\mathrm{Cr}}_2{\mathrm{O}}_7^{2-}$are respectively:
1. +5, +6 and +6
2. +3, +6 and +5
3. +5, +3 and +6
4. -3, +6 and +6

A mixture of potassium chlorate, oxalic acid and sulphuric acid is heated. During the reaction which element undergoes maximum change in the oxidation number?Redox Reactions

1. S

2. H

3. Cl

4. C

The correct order of N-compounds in its decreasing order of oxidation states is :

1. ${\mathrm{HNO}}_3,$ $\mathrm{NO},$ ${\mathrm{N}}_2,$ ${\mathrm{NH}}_4\mathrm{Cl}$

2. ${\mathrm{HNO}}_3,\hspace{0.17em}\mathrm{NO},\hspace{0.17em}{\mathrm{NH}}_4\mathrm{Cl},\hspace{0.17em}{\mathrm{N}}_2$

3. ${\mathrm{HNO}}_3,\hspace{0.17em}{\mathrm{NH}}_4\mathrm{Cl},\hspace{0.17em}\mathrm{NO},\hspace{0.17em}{\mathrm{N}}_2$

4. ${\mathrm{NH}}_4\mathrm{Cl},\hspace{0.17em}{\mathrm{N}}_2,\hspace{0.17em}\mathrm{NO},\hspace{0.17em}{\mathrm{HNO}}_3$

The correct example of metal displacement reaction among the following is: