(I) An antibody consists of four identical light (L) chains, and two identical heavy (H) chains.
(II) The stem 'Y' of antibody is called $F_{ab}$ fragment.
(III) The stem of the antibody and lower part of the arms constitute the constant 'C' region.
(IV) The portion of the antigen to which an antibody binds is called epitope.
The correct match is
$\begin {array} {1 1} (1)\;(II)\: and \: (IV) & \quad (2)\;(I)\: and \: (III) \\ (3)\;(III)\: and \: (IV) & \quad (4)\;(I)\: and \: (II) \end {array}$
