Prefix in word 'elongation' [closed]

Yes, it is a prefix although in its assimilated form because of the following consonant l.

The actual prefix is

ex-

word-forming element, in English meaning usually "out of, from," but also "upwards, completely, deprive of, without," and "former;" from Latin ex "out of, from within; from which time, since; according to; in regard to," from PIE *eghs "out" (source also of Gaulish ex-, Old Irish ess-, Old Church Slavonic izu, Russian iz). In some cases also from Greek cognate ex, ek. PIE *eghs had comparative form *eks-tero and superlative *eks-t(e)r-emo-. Often reduced to e- before -b-, -d-, -g-, consonantal -i-, -l-, -m-, -n-, -v- (as in elude, emerge, evaporate, etc.).

Etymonline

About elongation, the same dictionary says:

c. 1400, elongacioun, in astronomy, "angular distance of a planet from the sun as it appears from the earth;" early 15c., "extension, spreading," from Medieval Latin elongationem (nominative elongatio), noun of action from past-participle stem of Late Latin elongare "remove to a distance," from assimilated form of Latin ex "out" + longus "long".