Borax is a compound of boron and it`s often used as a cleaning product. It is chemically known as sodium borate.

Option 1 suggests that borax is prepared from calcium carbonate, but this is false because calcium carbonate doesn`t contain boron or sodium.

Option 2, magnesium carbonate, isn`t correct either. Although magnesium carbonate does contain carbonate, similar to borax, it lacks both sodium and boron.

Option 3, potassium carbonate, also turns out to be incorrect. Potassium carbonate does contain carbonate, but it lacks boron, one of the key components of borax.

Option 4 is the correct answer. Sodium carbonate, also known as soda ash or washing soda, is a common source for borax. Sodium carbonate can react with boron-bearing minerals in a process called borax fusion to produce borax. This supports the fact that borax is indeed prepared from sodium carbonate.