Which of the following is a common ignition source in a laboratory?

The selection of bunsen burners or electrical equipment as a common ignition source in a laboratory is accurate due to their frequent use and inherent risks. Bunsen burners are widely employed for heating substances and conducting experiments that require open flames. Their operation often involves flammable substances in the laboratory, which increases the likelihood of ignition if proper safety protocols are not followed.

Additionally, electrical equipment is ubiquitous in laboratories and can become an ignition source due to overheating, short circuits, or sparks generated during operation. This includes devices like stirrers, centrifuges, and various analytical instruments that rely on electrical power. Both bunsen burners and electrical equipment have direct connections to fire safety, making them significant considerations in a laboratory environment where flammable materials are present.

The other options, while they may represent potential ignition risks, do not compare in prevalence with bunsen burners and electrical equipment in most laboratory settings. Open flames alone are less common than various heated sources or electrical devices. Chemical reactions can indeed produce heat and potentially ignite flammables, but they are often controlled and monitored in laboratory procedures. Hot air from machinery might create a risk, but its role as a common ignition source is minimal compared to the hands-on usage and reliance on bunsen burners and electrical devices