Question

37. Which of the following changes are irreversible?
A. Lifting up a chair
B. Filling a glass with orange juice
C. Cooking a pot of rice
D. Bursting a balloon
(a) A and B
(b) B and C
(c) A and D
38. One of the following is not an irreversible change. This one is :
(a) ironing of clothes
(b) burning of incense stick
(c) baking of cake
(d) rusting of steel gate
39. Which of the following will lead to changes which cannot be reversed?
A. Addition of water to salt
B. Addition of water to cement
C. Addition of water to plaster of Paris
D. Pouring of water on hot iron rim of a cart wheel
(a) A and B
(b) B and C
please answer with explanation. ​

Answer 1

Answer:

It is because the bottom part is kept on fire which gives it a black colour.

The inner part also becomes black

sometime.

The outer part if cleaned thoroughly it won't be much black.