The table below gives some experimental results on four samples of water. Use the information to answer the questions that follow.
| Drops of soap needed to form lather |
| Sample of water (50cm2)|| Before boiling|| After boiling|
| A|| 25|| 15|
| B|| 8|| 8|
| C|| 18|| 8|
| D|| 25|| 25|
- Which sample(s) contain permanent hardness? Explain.
- Which samples are likely to contain calcium hydrogen carbonate? Explain.