Antibodies in our body are complex

In the structure of an antibody,the heavy chains and light chains are held together by which type of bond?

In the list given below,how many are secondary lymphoid organs?
Thymus,Spleen,Bone marrow,Tonsil,Appendix

$A$: A person who has received a cut accidentally and is bleeding needs to be given anti-tetanus treatment.
$R$: Anti-tetanus injection provides active immunity by providing preformed antibodies for tetanus.

What is an antibody?

The secretion of interferon is inhibited by . . . . . . .