Questions & Answers about La ceniza cayó al suelo.
Ceniza can be used as a mass noun in Spanish, just like ash in English. So la ceniza means ash in a general, uncountable sense.
- La ceniza cayó al suelo = The ash fell to the ground
- Las cenizas usually means ashes, often referring to separate remains, such as after a fire or after cremation.
So the singular here is completely natural.