Step 1: Understanding the Concept
Some hormones are named after the scientists who prepared them.
Step 2: Recall
J. B. Collip prepared an active parathyroid extract in 1925, so parathormone is called Collip's hormone.
Step 3: Why the others fail
Calcitonin lowers blood calcium, thyroxine controls basal metabolic rate and relaxin acts in pregnancy and parturition. None of these is linked to Collip.
Final Answer:
Collip's hormone is parathormone.
\[ \boxed{\text{(B) }\text{Parathormone}} \]