Which of the following can be used as an igniter to start a fire?

The selection of all options as potential igniters for starting a fire is correct because each listed item possesses characteristics that allow them to ignite or facilitate combustion under certain conditions.

Flashbulbs contain a flash powder that ignites quickly when an electric current passes through, producing a brief but intense burst of heat and light. This reaction can be sufficient to ignite flammable materials nearby, making flashbulbs a viable igniting source.

Black powder, also known as gunpowder, is a traditional form of explosive that burns rapidly, producing a significant amount of heat and gas. Its composition allows it to ignite other materials and initiate a fire, particularly when used in conjunction with a fuse or igniting mechanism.

Sodium reacts vigorously and exothermically with water, producing heat, hydrogen gas, and sodium hydroxide. The heat generated from this reaction can ignite the hydrogen gas, creating flames and potentially starting a fire.

Given the properties of each of these materials, they can all serve as igniters in various contexts, leading to the conclusion that all of them can be used to start a fire.