Answer: Option C. -> Orange juice is frozen to make ice lollies.
:
C
Changes that can be undone are called reversible changes. In the above-given options, only orange juice, which is frozen into ice-lollies, can be melted to give back the orange juice. So, it is a reversible change.
All of the other changes are irreversible.

Answer: Option A. -> reversible
:
A

A reversible change is a change which can be undone.
When a paper is folded to make a paper plane, we have changed the shape of the paper. But, it is not permanent. We can unfold the paper and bring it back to its original shape. This makes it a reversible change. 

Answer: Option A. -> People are using cars as a mode of transportation instead of a bullock cart
:
A and C

• Cars were not present in 348 BC but in 2017 people use cars as a mode of transportation so it's a change.


• Both in 348 BC and 2017 AD, his thirst is quenched by water so it's not a change.


• TV was not present in 348 BC but in 2017 it was a reality so it's a change.


• Cows used to graze fields in 348 BC and in 2017 AD also so it's not a change.

Hence, only the observations about the car and the TV are changes.

Answer: Option C. -> There is no such case possible in general.
:
C
Formation of curd from milk is an irreversible change, as milk cannot be obtained back from curd.
Melting of wax in a candle is a reversible change, as wax can be, solidified and can be converted back to a candle.
In general, changes around us are either reversible or irreversible.

Answer: Option A. -> Heating the iron ring
:
A
On heating the iron ring, it expands and so it becomes bigger in size. The wooden handle can go into the bigger hole. When iron rim is cooled it contracts and fits the wooden handle tightly. This same principle is used in many applications where a snug fit is required in metallic parts.

Answer: Option B. -> Helpful change - 1, 2; Non-helpful change - 3 
:
B

1.The farmers harvesting crop is helpful as the crops after processing give us grains, which are essential for nutrition and survival.

2.Ripening of fruits is helpful change as fruits become sweeter after they ripe and so become tastier.

3.Rancidity of food is non-helpful as food gets stale and not suitable for consumption.

Hence, all changes are not helpful.

Answer: Option B. -> False
:
B
Forest fires are irreversible changes. It is not possible to get back the forest in the exact same condition as before. Forest burns to produce some new material. These are ash and some gases. We cannot see these gases but can sense them due to their pleasant smell.

Answer: Option C. -> Change that can be undone is irreversible change and change that can't be undone is reversible change.
:
C

All the other points mentioned are correct except this. It should be: "Changes that can be undone are reversible change while the changes that can't be undone are irreversible change.”

For example, evaporation of water to become water vapour is a reversible change as it can be condensed back to water whereas baking bread is irreversible change as baked bread can't be unbaked.

Answer: Option B. -> True
:
B
A paper boat can be made from a paper and then by unfolding it, it can be converted back to the same paper. Thus, this is a reversible change. Melting of ice, folding of paper, water turning into vapour, inflation of balloon are some of the examples of a reversible change.

Answer: Option A. -> Irreversible and physical
:
A
$\bullet$ Changes which can't be reversed are called irreversible changes.
$\bullet$ The change in which the composition of the original substance remains unchanged and no new substance is formed during a change is called physical change.
$\bullet$ The figure depicts the cutting of an apple. Cutting of an apple is an irreversible change, as we cannot get the whole apple back in its original shape from the cut apple. It is also a physical change as apple's physical structure gets changed and no new product is formed in the process.