Final answer:
A day-old newborn's passage of meconium, a thick, greenish-black stool, is normal and the nurse should document this in the infant's record. It's a part of the normal physiological process for a newborn, and unless there are additional signs of complications, further action is not necessary.
Step-by-step explanation:
A day-old newborn passing a thick, greenish-black stool, known as meconium, is a typical occurrence indicating the baby is excreting substances ingested in utero. Since meconium passage is a normal part of the newborn's physiological process, the nurse should opt for A. Document the stool in the infant's record. This is the first and typical stool for a newborn and documenting it contributes to tracking the baby's development and health. If meconium is passed in utero, it may lead to complications, but in this scenario, there is no indication of an abnormal bowel movement being made before birth or of meconium aspiration syndrome. Hence, it does not require sending to the laboratory or notifying a practitioner unless there are other signs of distress or abnormality present.