Answer:

Introduction:
In this question, we are asked to identify a change of state that occurs due to heat gain. The given options include various changes of state, such as water becoming ice cubes, water in a pond becoming solid during winter, steam becoming water droplets on a metal lid, and ice becoming a puddle of water. We need to select the correct option and explain why it represents a change of state due to heat gain.

Explanation:
To determine the correct option, let's analyze each one of them:

1. Water becoming ice cubes in an ice tray:
- This is an example of a change in state from a liquid to a solid.
- However, this change is caused by the removal of heat energy (heat loss) rather than heat gain.
- Therefore, this option does not represent a change of state due to heat gain.

2. Water in a pond becoming solid during winter:
- This is an example of a change in state from a liquid to a solid.
- The change occurs as a result of heat loss, as the water cools down due to the decrease in ambient temperature during winter.
- Therefore, this option does not represent a change of state due to heat gain.

3. Steam becoming water droplets on a metal lid:
- This is an example of a change in state from a gas to a liquid.
- The change occurs due to heat loss, as the steam comes in contact with the cool surface of the metal lid and condenses into water droplets.
- Therefore, this option does not represent a change of state due to heat gain.

4. Ice becoming a puddle of water:
- This is an example of a change in state from a solid to a liquid.
- The change occurs due to heat gain, as the surrounding temperature rises and transfers heat energy to the ice, causing it to melt into a puddle of water.
- Therefore, this option represents a change of state due to heat gain and is the correct answer.

Conclusion:
Based on the analysis, option D - "Ice becoming a puddle of water" is the correct answer as it represents a change of state due to heat gain.