Of the two architects, one is experienced _______.

The correct completion for the sentence is "the other is not."

Explanation:

- "The other is not": This option correctly completes the sentence by indicating that one architect is experienced, while the other is not. It maintains parallel structure and provides a clear and concise expression of the comparison between the two architects.

- "The others are not": This option is grammatically incorrect because "others" suggests more than two architects, while the sentence specifies only two architects.

- "Another is not": This option is not suitable because it implies the presence of a third architect, which is not mentioned in the original sentence.

- "Another is inexperienced": This option changes the meaning of the sentence by introducing the concept of inexperience for one architect without directly contrasting their experience levels. It also doesn't maintain parallel structure with the phrase "experienced."

Therefore, "the other is not" is the most appropriate completion for the sentence, providing a clear comparison between the two architects' levels of experience.