All are steroids except ?

Ans. is 'd' i.e., Thyroxine Steroids Steroids are complex molecules consisting of four fused carbon rings. There is a phenanthrene nucleus made of three six-membered rings (A,B,C, rings), and a cyclopentane which forms D ring. The fully saturated parent compound (steroid) is known as cyclopentanoperhydrophenathrene. The alcohol derivatives of steroids, in which one or more OH groups are present in the steroids nucleus, are termed sterols, i.e. sterols are a class of steroids containing hydroxy (OH) group. Cholesterol, ergosterol, coprosterol and sitosterol are some impoant sterols.In animal tissues, Cholesterol is the major sterol. Functionally, cholesterol is a very impoant molecule being precursor of a variety of steroids -Steroid hormones :- Progesterone, estrogen, androgens (Testosterone), glucocoicoids, mineralocoicoids.Bile acids:- Cholic acid, Chenodeoxycholic acid.Vitamin DSo, all above mentioned compounds have cyclopentanoperhydrophenanthrene nucleus.