Element present in thyroxine is commercially produced fromALaminariaBPolysiphoniaCPorphyraDGelidium

Laminaria is a brown algae, commonly known as 'kelp'. It is a seaweed and used as food. It contains iodine and thus, used for commercial production of iodine. Iodine is a component of thyroxine hormone secreted from thyroid gland. Thyroxine is synthesised from iodine and tyrosine and secreted in body as T4 (Tetraiodothyronine) which may be converted to its active form T3 (Triiodothyronine) in liver and kidneys.

So, the correct answer is 'Laminaria'.