In human body, which one of the following hormones regulates blood calcium and phosphate?

Correct answer: Parathyroid hormone (PTH). PTH, secreted by the parathyroid glands, is a primary regulator of calcium and phosphate homeostasis in blood: it is released in response to falling serum calcium and acts to raise blood calcium while promoting phosphate excretion. In the kidney PTH increases calcium reabsorption and decreases phosphate reabsorption, producing net conservation of calcium and phosphaturia; in bone PTH increases bone turnover and releases calcium (and phosphate) from bone stores, with overall effect of increased serum calcium and decreased serum phosphate. These roles of PTH in calcium/phosphate regulation and its stimulation by low calcium are well established [3].

Sources

1. [1] https://www.sciencedirect.com/science/article/pii/S0896627323003914
2. [2] https://www.sciencedirect.com/topics/medicine-and-dentistry/parathyroid-hormone
3. [3] https://www.ncbi.nlm.nih.gov/books/NBK482128/