Answer: Option A. -> Chemical compositon changes
:
A and B
In chemical reactions, the chemical composition of the reactants changes resulting in new products.
The initial reactants cannot be obtained by simple physical means like filtering, sedimentation etc.
Chemical reactions are usually characterized by a chemical change, and they yield one or more products, which usually have properties different from that of the reactants.

Answer: Option D. -> rancidity
:
D
When food containing fats and oils come in contact with oxygen in the air, it undergoes oxidation. This causes bad smell and change in taste of food. This process is called rancidity.

Answer: Option D. -> Endothermic reaction
:
A, B, and C
The given reaction is a combination reaction because carbon and oxygen atoms are combining to form a carbon dioxide molecule.
In the given reaction, carbon is oxidised by gaining oxygen and thus oxygen is reduced. The reaction in which oxidation and reduction take place simultaneously is called as a redox reaction. So the given reaction is a redox reaction.
The given reaction is exothermic in nature since heat is released.

Answer: Option D. -> Small bubbles are formed
:
D
When zinc granules are added to dilute hydrochloric acid taken in a test tube, the zinc metal displaces the hydrogen from the acid and hydrogen gas comes out in the form of small bubbles. This is a displacement reaction. It occurs as follows:
$\mathrm{Zn}\left(s\right)+2\mathrm{HCl}\left(\mathrm{aq}\right)\to {\mathrm{ZnCl}}_2\left(\mathrm{aq}\right)+H_2\left(g\right)\mathrm{Zinc}\mathrm{Hydrochloric}\mathrm{Zinc}\mathrm{Hydrogen}\mathrm{acid}\mathrm{chloride}$

Answer: Option C. -> decomposition reaction
:
C
A decomposition reaction is where one reactant is broken into multiple simple products.
When lead nitrate $\left(2\text{Pb}{\text{(NO}}_3{)}_2\right)$ is heated, it decomposes into lead oxide $\left(\text{PbO}\right)$, nitrogen dioxide $\left({\text{NO}}_2\right)$ and oxygen $\left({\text{O}}_2\right)$. The reaction occurs as follows:
$2\text{Pb}{\text{(NO}}_3{)}_2\text{(s)}\stackrel{\text{Heat}}{⟶}2\text{PbO (s)}+4{\text{NO}}_2\text{(g)}+{\text{O}}_2\text{(g)}$
The reddish brown gas released is ${\text{NO}}_2$.

Answer: Option C. -> ${\text{Ca(OH)}}_2$
:
C
Slaked lime $\left({\text{Ca(OH)}}_2\right)$ is formed when quicklime $\left(\text{CaO}\right)$ reacts with water. The equation of the reaction is given below:

$\text{CaO(s)}+{\text{H}}_2\text{O(l)}\to {\text{Ca(OH)}}_2\text{(aq)}+\text{Heat}$

This is an example of a combination reaction because there is only one product that is being formed from the reaction between the two reactants.

Answer: Option A. -> $\text{Mg}$
:
A and B

A reactant is a substance that takes part in and undergoes the chemical reaction whereas a product is a substance that is formed as the result of a chemical reaction. Reactants are written on the left side of the arrow.

The reactants in the given reaction are magnesium $\text{Mg}$ and oxygen ${\text{O}}_2$. The product formed is magnesium oxide $\text{Mg}$ . 

Answer: Option A. -> Lead oxide
:
A and B
Lead nitrate on heating undergo thermal decomposition reaction to form a yellow residue of lead oxide, brown fumes of nitrogen dioxide and oxygen. The reaction occurs as follows:
$\underset{\text{Lead nitrate}}{2\text{Pb}{\text{(NO}}_3{)}_2\text{(s)}}\stackrel{\text{Heat}}{\to }\underset{\text{Lead oxide}}{2\text{PbO}\text{(s)}}+\underset{\text{Nitrogen dioxide}}{4{\text{NO}}_2\text{(g)}}+\underset{\text{Oxygen}}{{\text{O}}_2\text{(g)}}$

Answer: Option C. -> white precipitate of ${\text{CaCO}}_3$ is formed.
:
C
When ${\text{CO}}_2$ is passed through lime water, a white precipitate of ${\text{CaCO}}_3$ is formed, which turns lime water milky. The reaction occurs as follows:
${\text{Ca(OH)}}_2\text{(aq)}+{\text{CO}}_2\text{(g)}\to {\text{CaCO}}_3\text{(s)}\downarrow +{\text{H}}_2\text{O}\text{(l)}$

Answer: Option C. -> $2\text{Na(s)}+2{\text{H}}_2\text{O(l)}\to 2\text{NaOH(aq)}+{\text{H}}_2\text{(g)}$
:
A, C, and D

$\text{CaO(s)}+{\text{H}}_2\text{O(l)}\to {\text{Ca(OH)}}_2\text{(aq)}$ $CaO\left(s\right)+H_{2}O\left(l\right)\to Ca\left(OH{)}_2\right(aq)$

$2\text{Na(s)}+2{\text{H}}_2\text{O(l)}\to 2\text{NaOH(aq)}+{\text{H}}_2\text{(g)}$
${\text{H}}_2\text{(g)}+{\text{Cl}}_2\text{(g)}\to 2\text{HCl(g)}$
In the above chemical reactions, heat is released during the reaction. These type of reactions in which heat is either released or absorbed are called as a thermochemical reaction.

Moreover, the reaction of copper with zinc sulphate will not occur and the one mentioned is incorrect as copper is less reactive than zinc so it cannot displace zinc from its aqueous solution.