Aldosterone synthesis occurs exclusively in zona glomerulosa due to presence of:
18-hydroxylase (C) is the right choice. This sits at the heart of Endocrinology: the wording points straight to what is happening in the tissue or organ system. A useful study habit is to ask what the structure or process is for: cause and effect line up with 18-hydroxylase — that is the mechanism or reason the stem is pointing to. That reasoning supports 18-hydroxylase. One solid sentence about why this works is enough for recall — you do not need a long essay for every MCQ. When you practise, cover the choices first, write 18-hydroxylase from memory, then reveal the letter — that habit builds real recall for Endocrinology.
Ref: Animal physiology is Unit 7 of the CSIR NET Life Science Syllabus, covering core body systems. It accounts for roughly 10% of the total marks in Sections B and C.