The correct option is
B Thyroid
A. Thyroid gland is situated between the trachea and larynx in the neck and secretes thyroxine hormone which increases oxygen consumption by metabolically active tissues.
B. Parathyroid gland is present in the form of four small pouches which are embedded in the posterior surface of lobes of thyroid gland. This gland secretes parathormone which increases calcium reabsorption from the bones and causes mobilisation of calcium in the blood.
C. Adrenal cortex is part of adrenal gland and secretes glucocorticoids (cortisol,) mineralocorticoids (aldosterone) and sexocorticoids (androgens).
D. Gonads are sex glands that produces gametes. Male gonad is testis and female gonad is ovary.
Gull's disease, also known as Myxoedema, occurs due to deficiency of thyroid hormone in adults, after the mental and physical growth is complete.
So, the correct answer is 'Thyroid'.