Eustachian valve occur in –
A) Connection between middle ear and pharynx
B) Middle ear
C) Left ventricle of heart
D) Right Auricle of heart

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Hint: Eustachian valve is also known as valve of inferior vena cava. It is a remnant of fetal structure.

Complete answer:
A) Tympanic cavity (part of middle ear) is an air filled cavity that is connected with the nasopharynx through the Eustachian tube. It serves to equalize the air pressure in the tympanic cavity with that on the outside.
B) Middle ear – Ear ossicles are present here which are a flexible chain of three small bones, the malleus, the incus and the stapes. Middle ear is an air filled cavity that is a tympanic cavity that opens via the auditory (Eustachian tube) into nasopharynx.
C) Left Ventricle of heart – Left ventricle of heart receives oxygenated blood from the left auricle which is purified in lungs. It receives blood from the left atrium through a mitral valve from left ventricle blood is pumped to the body through aorta. It is the thickest chamber of the heart and is responsible for pumping oxygenated blood to further parts of the body.
D) Right Auricle of heart – It receives deoxygenated blood from the body through superior and inferior vena cava. This deoxygenated blood then enters into the right ventricle and from the right ventricle it will move to lungs for purification through the pulmonary artery. The Eustachian valve is a ridge of variable thickness in the inferior right atrium.

The correct option is D. Right auricle of heart.

Note:There is a difference between Eustachian tube and Eustachian valve. Eustachian tube is a canal that connects the middle ear to nasopharynx whereas the Eustachian valve is present in the heart (right atrium).