Which of the following is an essential pre-dive checklist item?

Checking air supply is a critical pre-dive checklist item because it directly affects a diver's safety and ability to complete the dive. Ensuring that there is enough air in the tank to reach the planned depth and return safely is paramount. Divers should know their tank's pressure and ensure that it meets the requirements for the dive duration they are planning. A thorough check of the air supply helps mitigate the risk of running out of air underwater, which can lead to dangerous situations, including emergencies that require surfacing quickly.

While assessing water temperature, reviewing dive history, and pairing with a dive buddy are also important aspects of dive preparation, they do not address the fundamental requirement of having sufficient breathing gas, which is vital for a diver’s survival underwater. In summary, checking air supply is essential for confirming that the diver can complete the dive safely and effectively.