Agglutinins are present in the . . . . . . .

Mature human $RBCs$ are enucleated. Which of the following is the most appropriate explanation for this?
$(i)$ They do not need to reproduce.
$(ii)$ They are somatic cells.
$(iii)$ They do not perform metabolism.
$(iv)$ Their internal space is available for $O_2$ transport.

What is the average number of erythrocytes per $mm^3$ of blood in a healthy human adult?

In leukemia (blood cancer),the number of white blood cells (WBCs) is -

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.

$A$ doctor suggested a couple not to have more than one child because: