**Core Concept**
The immediate treatment of tetany in an infant involves managing the underlying cause, which is often hypocalcemia. In infants, hypocalcemia can be due to various reasons such as maternal hypoparathyroidism, vitamin D deficiency, or excessive intake of phosphate. The treatment aims to restore calcium levels and alleviate symptoms.

**Why the Correct Answer is Right**
The correct treatment for tetany in infants involves administering calcium gluconate or calcium chloride to rapidly increase serum calcium levels. This is particularly crucial in infants where hypocalcemia can lead to severe complications. The intravenous administration of calcium helps to stabilize the nerve membrane and alleviate symptoms of tetany.

**Why Each Wrong Option is Incorrect**
**Option A:** Oral calcium supplements may not be effective in the acute setting, as they are absorbed slowly and may not provide immediate relief from tetany.
**Option B:** Vitamin D supplements alone may not be sufficient to treat tetany, as they require time to increase calcium absorption and levels.
**Option C:** Phosphate binders may actually worsen hypocalcemia by reducing calcium absorption, making this option incorrect.

**Clinical Pearl / High-Yield Fact**
In infants, tetany is often a sign of underlying hypocalcemia, which can be due to maternal hypoparathyroidism or vitamin D deficiency. Treatment with intravenous calcium gluconate or calcium chloride is essential to rapidly increase serum calcium levels and alleviate symptoms.

**Correct Answer:** C. Calcium gluconate or calcium chloride.