Which of the following terms is associated with a speech disorder often seen in infants?

The term "lallation" is directly associated with a speech disorder commonly observed in infants. It refers to the babbling or the repetitive sound-making phase where babies produce various syllables. This is a natural developmental stage in which infants experiment with vocal sounds, and it lays the foundation for future speech and language development. Observing this behavior is a sign that the child is developing communication skills and is often characterized by playful sounds that do not yet have meaning.

The other terms, while relevant in their respective contexts, do not pertain to speech disorders in infants. Juxtaposition refers to the comparison of two elements, often in literature or art; lanugo is a term used to describe soft, fine hair that covers an infant's body before birth; and ketoacidosis is a metabolic state resulting from excessive ketones in the body, usually seen in diabetic patients, not related to speech or communication. This contextual information helps to clearly differentiate why lallation is the appropriate choice regarding infancy and speech disorders.