Answer: Option B. -> False
:
B
Oxidation involves addition of oxygen or removal of hydrogen. Reduction involves addition of hydrogen or removal of oxygen.
For example:
$\text{C(g)}+{\text{O}}_2\text{(g)}\to {\text{CO}}_2\text{(g)}$
In this reaction carbon ($\text{C}$) is getting oxidised, whereas carbon dioxide (${\text{CO}}_2$) is getting reduced.

Answer: Option D. -> Iron nails dissolve completely.
:
D
When iron nails are added to an aqueous solution of copper sulphate, a displacement reaction occurs in which iron displaces copper from its solution which leads to fading of the blue colour of solution. After some time, the displaced copper settles down on the iron nails and reduces the surface available for reaction. So, the iron nailsdonot dissolve completely. The reaction involved is:
$\text{Fe}\text{(s)}+{\text{CuSO}}_4\text{(aq)}\to {\text{FeSO}}_4\text{(aq)}+\text{Cu (s)}$

Answer: Option C. -> Fe(s) + CuSO4(aq)→ FeSO4(aq) + Cu(s)
:
C
The reaction in which a more reactive element displaces a less reactive element from its compound or salt solution is called a displacement reaction.
Among the given options only in the reaction between iron and copper sulphate, iron $\text{(Fe)}$ being more reactivedisplaces copper $\text{(Cu)}$ from its solution.

Answer: Option C. -> AgNO3(aq)+NaCl(aq)→AgCl(s)+NaNO3(aq)
:
C
The reaction in which exchange of ions takes place between the compounds of the reactants is called adouble displacement reaction.
The reaction between silver nitrate and sodium chloride involves exchange of their ionic counter parts to form the product. Hence, it is a double displacement reaction.
All the other three reactions given are combination reactions. Combination reaction is a reaction in which two or more elements or compounds combine to form a new product.

Answer: Option C. -> endothermic
:
C
When potassium permanganateisheatedit produces potassium manganate, manganese dioxide, and oxygen gas. This means in the reaction heat is absorbed so it is an example of an endothermic reaction.
Exothermic reactions are those in which the heat is released.
Electrolysis is a process in which a substance undergoes decomposition by absorbing electrical energy.
Chemical reactions in which electrical energy is consumed are called electrochemical reactions.

Answer: Option D. -> (a) and (b) both
:
D
Often, a precipitate forms in adouble displacement reaction.In this reaction-
$AgN{O}_3+NaCl\to AgCl+NaN{O}_3$
both $AgN{O}_3$ and $NaCl$ exchange their ions to form new compounds, $AgCl$ (ppt) and $NaN{O}_3$. Hence, it shows both double displacement and precipitation.

Answer: Option B. -> Rusting of iron
:
B
Rusting of iron is a chemical reaction. Whenironrusts, it reacts with oxygen present in water or moisture in the air to create a new compound callediron (III) oxide.
$Fe\left(s\right)+O_2\left(g\right)\to F{e}_2{O}_3.x{H}_{2}O\left(s\right)$
$F{e}_2{O}_3.x{H}_{2}O$is commonly known asrust and has properties entirely different from that of iron or oxygen.
Other options involve either change in physical state or size.

Answer: Option D. -> NH3(s)+HCl (aq)⇋NH4Cl (s)
:
D
While writing a chemical equation letter are used in brackets or subscripts next to the chemical formulaeto specify the physical state of the reactants and the products.
- s is for solids
- l is for liquids
- g for gas
- aq is aqueous solution
Thereactionin which the physical state of the reactants or the product is not correctly represented is:
${\text{NH}}_3\text{(s)}+\text{HCl (aq)}\leftrightharpoons {\text{NH}}_4\text{Cl (s)}$
This is because ammonia$\text{(}{NH}_3)$is a gas.

Answer: Option C. -> Hydrogen gas and iron (III) chloride are formed
:
C
In an aqueous solution, the hydrochloric acid dissociates to render hydronium ions and chloride ions. The released chloride ions oxidize the iron atoms to form iron (III) chloride as ${\text{Fe}}^{3+}$ ions are more stable than${\text{Fe}}^{2+}$ ions. The hydrogen ions are reduced to hydrogen gas. Here, the reduction is observed in terms of the gain of electrons and the oxidation is observed in terms of the loss of electrons.Hence,hydrogen gas and iron (III) chloride are produced.

Answer: Option B. -> Combination reaction
:
B
In combination reaction, two or more elements or compounds react to form a single product. The given reaction is a combination reaction as carbon and oxygen are combining to form carbon dioxide.