Cords of Billroth are blood-filled spaces found in which of the following organs?

Which of the following organs is known as the blood bank of the body?

Which of the following vertebrate organs receives only oxygenated blood?

Assertion $A$: In an open circulatory system, the blood volume is high, but the blood pressure is low and irregular.
Reason $R$: In a closed circulatory system, the blood volume is limited, and the blood pressure is high and regular.
Which option is correct for Assertion $A$ and Reason $R$?

Which of the following is correct regarding blood coagulation?
$I$. Vitamin-$K$ is necessary for the formation of prothrombin.
$II$. Conversion of fibrinogen to fibrin is done by thrombin.
$III$. Conversion of prothrombin to thrombin is done by the enzyme complex prothrombinase.
The option with the correct combination is:

The $pH$ of blood in an artery and a vein is: