Which is not true about thyroxine?

Question

$\begin{array}{1 1} (a)\; \text{Iron is essential for synthesis of thyroxine} \\ (b)\; \text{It regulates carbohydrates, fat and protein metabolism} \\ (c)\; \text{Thyroxine gland requires iodine to synthesize thyroxine} \\ (d)\; \text{Thyroxine when secreted below the normal levels results in hypothyroidism} \end{array}$