Read the table carefully and answer the following questions:
A student observed the following activities during a science exhibition.
| Activity | Observation |
|---|---|
| A | Ice changed into water after being left outside for some time |
| B | An iron nail developed a reddish-brown coating after being exposed to air and moisture for several days. |
| C | Clay was moulded into the shape of a toy elephant. |
| D | A sheet of paper was burnt completely, leaving behind ash and smoke. |
1. Which of the following activitiy is an example of a change in state?
2. Which activity is most likely reversible?