Which of the following changes can be reversed by changing the temperature: (a) dew condensing on a leaf; (b) an egg turning hard when it is boiled; (c) ice cream melting; (d) a spoonful of batter cooking on a hot griddle?

(a) dew condensing on a leaf

(c) ice cream melting

Explanation:

The process which can be reversed by changing the temperature , i.e. , by increasing or decreasing the temperature , is called the reversible process .

From the question ,  

As the water on the leaf can be changed to gaseous state by increasing the temperature .  

The process of condensation and evaporation are reversible of each other .

The melted ice cream can be solidified again by reducing its temperature , hence , it is a reversible process .

They both are irreversible process , and by changing the temperature , we can not get back the original substance .

c. 4.54 x 10–12 j happens to be correct