Identify clustering problems

Which of the following are clustering problems?

1. Determining how many features it takes to describe most of the variability in data
2. Determining the natural groupings of houses for sale based on size, number of bedrooms, etc.
3. Visualizing 13 dimensional data (data with 13 features)
4. Determining if there are common patterns in the demographics of people at a commerce site
5. Predicting if someone will click on a web advertisement