Which tube has no additive?

The white top tube is correct as it typically contains no additives. These tubes are often used for collecting blood or other samples that do not require any anticoagulants or preservatives, making them suitable for certain types of testing, such as serum collection.

In contrast, each of the other tubes mentioned contains specific additives to facilitate different types of tests. For example, the blue top tube usually contains sodium citrate, which acts as an anticoagulant to prevent blood from clotting and is primarily used for coagulation studies. The lavender top tube contains EDTA (ethylenediaminetetraacetic acid), which is also an anticoagulant but is used mainly in hematology for complete blood counts. The green top tube typically contains heparin, another anticoagulant, and is used for certain blood chemistry tests.

Therefore, the white top tube's lack of an additive makes it distinct and suitable for specific applications that require unaltered serum.