Answer: Option A. ->
:

Definition: 1 Mark
Factors: 2 Marks
Preventive measures: 2 Marks
Rust is a reddish- or yellowish-brown coating of iron oxide that is formed on iron or steel by oxidation, especially in the presence of moisture.
 

The presence of water and oxygen is essential for the rusting of iron. However, Impurities in the iron, the presence of water vapor, acids, salts and carbon dioxide hasten rusting. Again, pure iron does not rust in dry and carbon dioxide free air. It also does not rust in pure water, free from dissolved salts.
$Iron\left(Fe\right)+Oxygen(O_2,fromtheair)+water\left(H_{2}O\right)\to Rust\left(ironoxide\right)(F{e}_2{O}_3.H_{2}O)$
The various measures that can be taken to prevent rusting of Iron are: 
i) Galvanisation: It is the process of deposition of a layer of zinc on iron. It prevents rusting of iron.
ii) We can apply a coat of paint or grease on iron.

Answer: Option A. ->
:

Option a) Identification and Explanation of each change: 1.5 Marks
Option b): 2 Marks
a) LPG is in a liquid state inside the cylinder. However, when it comes out of the cylinder it becomes a gas. So, it is a physical change, because no new substance is formed. It is only a change in state.
When the gas comes out and burns, it is a chemical change, because the LPG gas burns with oxygen and forms carbon dioxide. Heat is also released while burning the gas.
So, change A is a physical change while change B is a chemical change.
b) The ozone layer protects us from harmful ultraviolet rays which come from the sun. Ozone absorbs this radiation and breaks it down into oxygen. In this process, a new substance is formed, so it is a chemical change. If the ultraviolet rays are not absorbed by the ozone layer, these harmful rays would reach the earth's surface and cause harm to us and other life forms.

Answer: Option A. ->
:

Each step: 1 Mark
Following are the steps for the formation of copper sulphate crystals:
(i) Take a cupful of water in a beaker and add a few drops of sulphuric acid into it.
(ii) Heat the water and add copper sulphate powder slowly into it.
(iii) Continue adding copper sulphate powder till no more copper sulphate can be dissolved.
(iv) Filter the solution and allow it to cool.
(v) After some time, when the solution has cooled down, clear crystals of copper sulphate will be visible.

Answer: Option B. -> False
:
B

This statement is false as global warming is caused by increasing amount of carbon dioxide gas.

Answer: Option A. -> physical
:
A
The change in which chemical properties of the original substance remains unchanged and no new substance is formed is called physical change.
Dissolution of sugar in water is a physical change because it does not result in the formation of a new substance. It is a reversible change as sugar and water can be extracted back from the solution.

Answer: Option A. -> True
:
A
The change due to which the one substance is transformed into another substance having new and different chemical properties is called a chemical change.
Curdling of milk is a chemical change as a new substance (curd) is formed which has different taste, form, properties and it cannot be converted back to milk.

Answer: Option A. -> True
:
A

Burning of wood is a chemical change in which a new substance along with heat is produced whereas cutting of wood into small pieces is a physical change as it does not result in the formation of a new substance with different chemical properties. Hence, the given statement is correct.

Answer: Option C. -> Burning of wood
:
C

When we light the wood up, it burns gently and after a while, it turns into ashes. As it burns, it produces heat, light and smoke which escapes through the chimney. The heat, light, fire and smoke are all good characteristics of a chemical change, which result in a completely new matter i.e. ashes. In the other options like cutting of wood, melting of ice and dissolving sugar in water, no new substances are formed. So, these are examples of physical changes. 

Answer: Option B. -> Content of moisture in air is high in rainy season whereas air is almost dry in summer season.
:
B

Content of moisture in air is high in rainy season whereas air is almost dry in summer season. For rusting, the presence of both oxygen and water is essential. Rusting becomes faster, if the content of moisture in air is high. Hence, rusting of iron objects is faster in rainy season than in summer season. 

Answer: Option B. -> Flammability
:
B

Physical properties can be observed or measured without changing the composition of matter. They are used to describe matter.
Physical properties include appearance, texture, colour, odour, melting point, boiling point, density, solubility and many others. Flammability is a chemical property of a substance.