The pro-condition for transfusion of blood to an accident victim is

Step 1: Analyze the question "Pro-condition" here means a prerequisite, something that must be done before a blood transfusion can safely take place.

Step 2: The concept Human blood is grouped as A, B, AB or O, based on antigens on the red blood cells and antibodies in the plasma. If incompatible blood is transfused, the recipient's antibodies attack the donor's red blood cells. This causes agglutination (clumping), which can block blood vessels and lead to kidney failure or death.

So before any transfusion, the blood groups of the donor and the recipient must be tested and matched (cross-matching) to confirm compatibility.

Step 3: Check each option

• A. Assess the level of blood lost: Useful for deciding how much blood is needed, but it does not make the transfusion safe.
• B. Boil the blood: Heat destroys the blood cells and proteins, so the blood would be useless.
• C. Cross-match the victim's and donor's blood groups: Correct. It prevents agglutination and transfusion reactions.
• D. Mix with sulphur: Meaningless and harmful. (Anticoagulants like sodium citrate are used to store blood, not sulphur.)
• E. Remove the victim's remaining blood: Dangerous, since the victim has already lost blood.

Step 4: Answer The essential prerequisite is cross-matching the blood groups of the victim and the donor, which is option C.

Tip: Remember "Match before you transfuse." Whenever a question asks about a condition for transfusion, think of blood group compatibility first. Also remember that O is the universal donor and AB is the universal recipient (in the ABO system).