Which is a common drying agent used in organic chemistry?

Anhydrous magnesium sulfate is widely recognized as a common drying agent in organic chemistry due to its effectiveness in removing water from organic solvents and reaction mixtures. It has a high affinity for water, allowing it to absorb moisture efficiently. This property is particularly useful in the preparative processes of organic chemistry, where the presence of water can interfere with reactions or affect yields.

When an organic solution is treated with anhydrous magnesium sulfate, it forms a hydrate, thus dehydrating the mixture. The use of magnesium sulfate is advantageous because it is relatively inexpensive, non-toxic, and does not react with most organic compounds. After it has absorbed water, it can be removed by filtration or decantation, facilitating the isolation of the desired organic products.

In contrast, other substances listed do not serve the same purpose or have the necessary properties to be effective drying agents in organic chemistry, which is why they are not suitable answers.