Which of the following is an example of a pyrophoric material?

• A. Ammonium nitrate
• B. Water
• C. Sodium chloride
• D. Aluminum alkyls

Answer: (D)

Pyrophoric materials ignite spontaneously in air at room temperature. Aluminum alkyls are classic examples because they react violently with oxygen and moisture in the air, releasing heat quickly enough to ignite without any external ignition source. This high reactivity is why these compounds must be handled under inert atmospheres and with stringent moisture control, as even tiny exposures can start a fire.

In contrast, ammonium nitrate is a strong oxidizer and can detonate under certain conditions, but it does not ignite on its own in air. Water is nonflammable and can extinguish many fires. Sodium chloride is a stable salt with no flammable properties.