Which blood group is considered the universal recipient?

Clotting disorders occur because:

The $pH$ of human blood varies between

Choose the incorrect sentence$(s)$.
$(I)$ $RBCs$ are formed in the white bone marrow in adults.
$(II)$ $RBCs$ have a red colour because of the presence of a protein called haemoglobin.
$(III)$ The nucleus is present in $RBCs$ in most mammals,and they are biconcave in shape.
$(IV)$ $A$ healthy individual has $12-16 \, g$ of haemoglobin in every $100 \, ml$ of blood.

The most well-known blood grouping is the $ABO$ group,named as $ABO$ and not $ABC$,because '$O$' in it refers to having:

Highest content of iron is found in