Vortex already is a singular form. The plural can be vortexes or vortices. Both are equally correct.
The singular form of vortex is "vortex" and the plural form is "vortices."
The plural form of vortex is vortices.
Phenomenon is the singular form of phenomena.
The noun quantum is the singular form; the plural is quanta.
The singular form of "rays" is "ray".
The singular form of vortex is "vortex" and the plural form is "vortices."
The noun vortex is a singular, common noun, a word for whirling fluid or air, a thing.
The plural form of vortex is vortices.
The singular form of the demonstrative pronoun 'these' is this.
The singular form of "that" is "it."
it is already in its singular form.
The singular form is cuff.
"Stratum" is the singular form of stratum. The plural form is "strata".
The form hypothesis is the singular form. The plural form is hypotheses.
A singular form of dice is a die
The singular form of feet is foot.
The singular form of Oases is, Oasis.