Select the word that is spelled INCORRECTLY.

Concept

Spelling-error questions test whether a word matches its standard dictionary form. A word is spelled correctly only when every letter of its accepted form is present and in the right order; dropping, adding, or transposing even a single letter makes it incorrect. To find the odd one out, compare each candidate against the word it is meant to be.

Application

Checking each candidate against its standard form:

So the word that fails the dictionary check is Outflo, which should be spelled Outflow.

Cross-check

Restoring the missing letter turns the broken form into Outflow (the movement of liquid, money, or air out of a place), confirming that exactly one letter was missing. The other three already appear in the dictionary unchanged, so each of them is spelled correctly.