Final answer:
Red top tubes should not be placed on a blood rocker because they are designed for blood to clot naturally and rocking would disrupt this process.
Step-by-step explanation:
To answer the question: Red top tubes should never be placed on a blood rocker. These tubes typically contain a clot activator and are used for serum chemistry tests. The purpose of a red top tube is to allow blood to clot naturally, so placing it on a rocker would disrupt this process. Green top tubes contain heparin, blue tops contain sodium citrate, and purple tops contain EDTA; all of these anticoagulants require gentle mixing on a rocker for accurate diagnostic testing.